“A submarine … sighted an enemy task … [and] failed to attack. It is most regrettable. I am beginning to feel that the words of those who say the submarine is only good for raiding operations and scouting are almost admissible. I wish they would strike enemy warships even once just to disprove them.” — Admiral Matome Ugaki, Fading Victory
Failing to reach the goal of winning a “decisive battle” at Midway or Guadalcanal, the Japanese continued to focus on hunting for the elusive striking victory.{137} The Japanese submarine force was riding a wave of success as they had had some influential sinkings during operations around Guadalcanal. The combat power of Japanese submarine force was diluted through numerous commitments in the Indian and Pacific Oceans and the crest of submarine success was passing. The Sixth (Submarine) Fleet would embark on a series of campaigns to attempt to stunt the ever present advance of American forces across the Pacific.
The Japanese Navy viewed the occupying forces on the islands of Attu and Kiska in the Aleutian chain as an impetus to draw significant American forces into the area for a potential precursor to the “decisive battle.” In early 1943, the Japanese had seven submarines of varying capabilities operating in the Aleutians. Six of these were medium range RO-class boats. The Japanese detected American Admiral Thomas Kinkaid’s invasion fleet transiting towards the area in May 1943. With the departure of all Japanese surface forces because of significant losses in the Battle of the Komandorskis (27 March 1943), submarines were left as the final challenge to the American invasion and the single source of supply to the garrisons. Two submarines, I-31 and I-35, managed to penetrate the protective screen of the invasion fleet, but they were unable to take advantage of the position and sink anything. Both boats survived the effort even though I-35 would soon be damaged and I-31 sunk.{138}
Admiral Mineichi Koga, successor to command of the Combined Fleet when Admiral Yamamoto was killed, believed that a “decisive battle” in the near future was the sole chance for success of the Japanese Navy. Sensing the opportunity for a major battle that could weaken American combat power, eight further submarines were rushed from the Central Pacific to the Aleutians. The submarines transferred to support operations in the Aleutians were not equipped for cold weather operations. All submarines needed to return to their home bases in Japan simply to swap clothes and other items to protect personnel in cold weather. The submarines lacked radar to assist in operations in the reduced visibility regularly encountered. This compounded the threat of enemy action with the threat of navigational problems caused by persistent fog and harsh weather.{139}
Eight submarines would be committed to supply operations before the decision was made to abandon the islands. With this decision, thirteen submarines took on the role of evacuation transports. At this point in the war, two-thirds of available submarines were committed in supply or defensive roles throughout the Pacific Ocean. Fifteen successful supply/evacuation runs were completed to Kiska, providing 125 tons of supplies and retrieving 820 soldiers. The supply and evacuation operations led to the loss of three submarines in two weeks. The commander of the operation allowed no further direct participation of submarines based on these results.{140}
With the abandonment of supply and evacuation operations, submarines in the Aleutians continued to support the campaign mainly through reconnaissance missions. The final cost of submarine operations in the Aleutians was steep. American forces sank five submarines: I-7, I-9, I-12, I-24, and I-31. Two submarines, I-2 and I-157, ran aground and were lost for further operations. Exemplary of the unique conditions of the area of operations, I-155 sustained severe damage in a storm and returned to Japan. For the commitment and loss of so many submarines, the Japanese failed to sink any ships, nor did they slow the invasion of Attu and Kiska. The lone positive result for the submarines was the small number of experienced pilots that were evacuated to return to Japan for reassignment.{141}
The failure of the submarines to stop, or even slow, the American invasion in the Aleutians was a result of the poor employment of the vessels. The submarines sent to the Aleutians lacked proper equipment to allow them to operate there successfully. They were not organized to focus their combat power on the invasion fleet. They were tasked to conduct a mission for which they were ill suited and untrained. The fact that the submarines were not released from this operation immediately once it became an evacuation mission is unconscionable when one considers that the force was already stretched thin across two oceans.
The number of losses in the harsh conditions of the Aleutians did drive a change in the policy of the Naval General Staff with respect to radar. Prior to these losses, both to enemy action and navigational issues, the Naval General Staff did not view the inclusion of radar on submarines as a priority. After the Aleutians campaign concluded, all submarines were ordered to be fitted with radar immediately.{142}
The lack of a concerted anti-submarine effort by the Allies allowed Japanese submarines to continue to roam free in the Indian Ocean. Early in 1943, the force of eight submarines was limited to three by the need for overhauls. These three subs still managed to sink seven ships while damaging another. As 1943 continued, six active submarines were able to sink sixteen vessels while damaging a further five.{143}
Operations in the Indian Ocean are unique because they marked the only time that German and Japanese forces conducted coordinated operations during the war. By the end of 1943, eight Japanese submarines and seven German submarines operated in the Indian Ocean along with various surface raiders and supply vessels. The Germans built their own submarine bases, such as Surabaya, Java, as the size of the Axis effort in the Indian Ocean was too large for the Japanese bases alone.{144}
Over time, the Allied anti-submarine effort in the Indian Ocean grew. With greater opposition, Japanese results started to dwindle. Large numbers of escorts arrived and protective measures were implemented for merchant vessels. Two submarines were sunk, I-27 and RO-110, while the rest conducted a small number of successful patrols. In the first half of 1944, Japanese submarines sank a dozen vessels and damaged another to counter their two losses. As pressure grew in the Pacific, all submarines, except for two of the RO-class boats, were withdrawn from the Indian Ocean. From the middle of 1944 to the end of the war, only one more Allied merchant was sunk in the Indian Ocean by Japanese submarines.{145}
One of the few successful submarine patrols in the Indian Ocean in the first half of 1944 was completed by I-8 commanded by Commander Ariizumi. Ariizumi led the I-8 to four sinkings (although one was a small sailing vessel) but two of the sinkings show the result of the frustration of the failing Japanese war effort. The Dutch merchant Tjisalak and the American merchant Jean Nicolet were victims of I-8. The crew of I-8 tortured and murdered nearly two hundred survivors from these two vessels.{146}
The Japanese submarine operations in the Indian Ocean provide clear evidence of their ability to conduct commerce raiding successfully. Their success in this theater must be understood in context however. The Indian Ocean was an extremely permissive environment for submarine operations due to the failure of Allied nations to commit sufficient anti-submarine effort to the theater. Once these assets arrived, Japanese successes decreased considerably. The pressures of the American advance in the Pacific also required the departure of most submarine assets from the Indian Ocean verifying its standing as a secondary theater of operations. The Japanese commitment to the area never grew past the high mark of eight. Had the Indian Ocean been more important to the war effort, more submarines would have been sent. The Indian Ocean instead acted to deprive assets from actions where they could have proved useful. While an interesting sidelight, the coordinated operations of the Germans and Japanese did not indicate that they Indian Ocean was a major theater of operations vital to any war plan.
The real importance of the Indian Ocean operations was twofold. First was the ability to train crews and ready them for the greater challenges of operations in the Pacific Ocean. Officers sent to boats in the Indian Ocean were able to expand on the knowledge gained in training through practical exercise. They were able to experiment and learn with minimal risk to themselves or their crew. Operations in the Indian Ocean also proved the superiority of Japanese submarine design. The boats were able to take advantage of their long range and large size to conduct extended patrols covering large amounts of the Indian Ocean. They were able to cross the Indian Ocean with ease from their bases to conduct patrols at the southern terminus of the Red Sea. Their superior torpedoes also meant that most of the merchant sinkings were completed with a single weapon. Despite these positives, the Indian Ocean operations stood as an example of imprudent use of limited assets since no country’s war effort was dependant on control of the Indian Ocean.
As the American offensive continued in the South Pacific in the middle to late 1943, Japanese submarines continued to conduct mogura (supply) operations to re-provision cut off garrison troops. Even though Admiral Takeo Takagi, commander of Sixth (Submarine) Fleet, would promise a return to offensive operations when he took command in November 1943, numerous submarine commanders complained heavily about the continuation of supply operations with minimal offensive patrols before and after his arrival. Even though orders would come that started to task submarines with attacking American rear supply lines, supply operations occupied the primary mission in the Solomons.{147}
The distaste for supply operations did not cause the submarine commanders to devote less effort to them. Enterprising commanders recognized the Allied operating cycle and adjusted their operations accordingly. With the adjustments, Japanese submarines spent more time submerged at night than before only coming up to charge batteries at dawn and dusk. The increased submerged time further limited the ability of a small force to search appreciable amounts of sea area in their adjunct reconnaissance tasking.{148}
As the commander of I-177, Commander Zenji Orita would complete fourteen supply runs from New Guinea to Rabaul. This was possible because the previously discussed ingenuity of commander and the predictability of Allied efforts. The boats preparing for transport runs were able to submerge in the harbor during the daily American attacks and continue loading during the remainder of the day. This counter to the predictability of the American attacks did not cause the Japanese to recognize the risk inherent in their own repetitive operations. Instead, the Japanese clung to their own repetitive and predictable cycle of operations in both supply operations as well as scouting operations.{149}
Even when they managed to survive the ever-increasing American air raids and anti-submarine forces, Japanese submarines were still not able to conduct offensive operations when conducting supply operations. Orders strictly forbade conducting torpedo attacks while on supply runs. The only exception was if the observed target was either a battleship or aircraft carrier. Even with the freedom to attack these ships, commanders would avoid these opportunities to complete the supply mission. Commander Mochitsura Hashimoto, when in command of RO-44 near Mejuro, observed a number of battleships and aircraft carriers within a few hundred yards one night.
Instead of pressing an attack with the torpedoes that he already had prepared, he chose to avoid action and not endanger his supply and reconnaissance mission. When admonished by his superiors on return from the mission, he simply responded that he did not want to endanger completing the mission.{150}
Submarines were moved en masse to the central Solomon Islands to counter the American invasions following the loss of Guadalcanal. Despite the large number of submarines employed, a very small number of ships were sunk. From late 1943 through early 1944, seven submarines were lost for a tally of only three sinkings. This did not mark an auspicious start to the newest re-focusing of the submarine effort to wear down enemy forces in the central and south Pacific Ocean.{151}
The American offensive into the Gilbert and Marshall Island chains was the first opportunity for Takagi to oversee the operations of the Japanese submarine force. Based on the large number of losses in Japanese surface and air forces prior to this offensive, submarines were the only forces available to counter the attacks towards Tarawa and Makin Islands. Nine submarines were available for assignment and they were moved immediately. The small number of submarines available for employment would limit the results of the effort as much as Takagi’s lack of experience would. Takagi’s assignment as Sixth (Submarine) Fleet commander followed the trend of assigning flag officers to this position even though they had little or no recent experience with submarine operations.{152}
The submarines formed picket lines on 19 November. The initial arrangement of the nine submarines formed five circles to create a layered defense. From 19 November through 30 November, picket lines were shifted on an almost daily basis with at least one instance of three shifts occurring in a two-day period. Takagi attempted to simulate a much larger force with the nine submarines that he had available. The submarines were put through a series on confusing and contradictory orders that involved high-speed surface runs and random radio transmissions to generate the ruse of a larger force.{153} The effectiveness of the Japanese submarine force to this point in the war did not support the ruse. Combined with the lack of a surface threat in the area and limited air assets, the American force was not deterred. The random movements and false transmissions only served to draw the submarines away from any real results while placing them at greater risk.
The only people that Takagi’s simulation was able to influence were his own submarine commanders. Submarine commanders felt that Sixth (Submarine) Fleet’s random orders placed the submarines at great risk and directly influenced the loss of six submarines out of the nine assigned to the area. The assignment of submarines failed to take advantage of the inherent strengths of the submarine as well as failing to cover their faults. The submarines were not allowed to analyze their operating areas and adjust to the Allied operating cycle. Instead, the submarines were forced to expose themselves in high-speed surface transits at all times of day regardless of the threat.{154}
Operations attempting to defend the Gilbert Islands from invasion were costly. Six submarines were lost. These losses caused the Combined Fleet to avoid committing further submarine assets to the Marshall Islands area. While no submarine defensive operations were conducted in the vicinity of the Marshalls, the lack of surface assets ensured that the invasion force was unopposed at sea. Two submarines did conduct operations in the area, but they were tasked in a piecemeal fashion to recover aviators for later operations.{155}
For the cost of six of their own, the Japanese submarines operating in the Gilbert and Marshall Islands were only capable of sinking a single vessel. On 24 November, Lieutenant Commander Sunao Tabata, in command of I-175, sighted an American aircraft carrier. A full salvo of six torpedoes was launched at the target. The American escort carrier USS Liscome Bay sank twenty-three minutes after a single torpedo from the salvo struck. The loss of the Liscome Bay did not influence the American invasion of the Marshall and Gilbert Islands, but the manner of its sinking did underline the capability of the Japanese torpedoes. Loss of the Gilbert and Marshall Island chains also meant the loss of Kwajalein, the original forward base of submarine operations during the war.{156}
During the time of operations in the Gilbert and Marshall Islands, the I-176 was assigned to conduct security patrols near the Japanese base at Truk. I-176 was not one of the nine boats assigned to the main effort to stop the invasion. During the course of the patrol, I-176 performed a unique event for the Japanese submarine force. On 16 November 1943, I-176 fired a salvo of three torpedoes at an American submarine. Two hits sank the USS Corvina. This would be the only loss of an American submarine to a Japanese submarine during the entire war. This finally gave the Japanese a submarine victory over an American submarine.{157}
The comparison of submarine versus submarine results is potentially dubious as an evaluation of effectiveness of different submarine forces in World War II. That being said some important things could be gleaned from the comparison. The Japanese submarine force sank three submarines, only one of which was American, as previously mentioned. The American submarine force sank twenty-three submarines and all but two of them were Japanese. The British submarine force sank 36 submarines. Of these 36, sixteen were German, eighteen were Italian, and the final two were Japanese. Of the 62 sinkings by Japanese, American and British submarines in submarine on submarine interactions, all but one had the target operating on the surface.{158}
While the results of submarine on submarine action do not provide insight into any advanced tactics, the comparison of American and Japanese results against one another do indicate the opposing uses of submarines. Had the Japanese submarines been employed on offensive operations, their operations would not have been as scripted as the recurring supply runs that allowed them to be easily intercepted. The overdependence on communications up and down the command chain exposed the Japanese submarines to interdiction. The American submarines were less vulnerable based on the concern for operational security. The decentralized control of the American submarine force ensured far greater security in the execution of their assigned tasks. The American successes highlight the more open and offensive manner in which they were employed.
The actions in the Gilbert and Marshall Island chains spanned the closing of year. The year 1943 did not have the same level of success that submarine force enjoyed in the previous year. Twenty nine submarines were lost during the course of the year. Fifty six merchants were sunk at the hands of Japanese submarines. The majority of these were sunk in the Indian Ocean. Only a small handful of warships were sunk, none of which that could be considered major combatants. One escort carrier and one submarine were sunk. Two torpedo boats and a tank landing ship (LST) were also sunk. The only other success against a warship occurred against the Australian cruiser HMAS Hobart that was put out of action for seventeen months by a single torpedo hit.{159}
Japan started 1944 with the largest force of submarines available of any year during the war. The 66 operational submarines were divided between 42 large I-class boats and 24 medium and small RO-class and HA-class boats. The primary roles defined by the senior staff were merchant attacks and supply/evacuation operations. Supply operations would continue to dominate efforts.{160} Even with the favorable force size at the beginning of the year, the command structure that limited it was still firmly entrenched and would not change without the aid of a catastrophic setback.
With the loss of the Gilbert and Marshall Island chains, the Japanese were forced to fall back further in their defensive posture. The Americans turned bases in the Marshall Islands into resupply and formation centers for further thrusts into the Japanese defenses. In an attempt to gain intelligence on American force structure and intentions, the Japanese sent eight different submarines on reconnaissance patrols into the Marshall Islands early in 1944. While no boats were lost in these attempts, they were all unsuccessful at penetrating the American anti-submarine screen and gathering any useful information.{161}
The loss of the Gilberts and Marshall Island chains exposed the Japanese naval bastion of Truk to concentrated attacks from both American air and surface assets. Submarines were specifically maintained in the Central Pacific to warn of American carrier movements. Ironically, these submarines failed to give any warning of attacks in February 1944 that crippled Japanese submarines’ forward operations. During one raid, the submarine tender, and current fleet flagship, Heian Maru was sunk. With the sinking, the Sixth (Submarine) Fleet lost the majority of its repair parts and specialized equipment. The former flagship of the fleet, the cruiser Katori, was also sunk by American surface vessels as it tried to depart Truk. With these losses, the Sixth (Submarine) Fleet was forced to shift all submarine assets and repair/upkeep work to bases in the Home Islands. The forward command base for the submarines, which had moved to Truk when Kwajalein became untenable, was forced to move again. Takagi moved with his staff to Saipan to continue to coordinate operations.{162}
With the collapse of the Japanese defensive perimeter bounded by the Bismarck, Gilbert and Marshall Island chains, Operation A-Go was crafted as an attempt to stop the American advance into the area that the Japanese called the imperative zone. The operation was another attempt at a “decisive battle” to blunt the American drive through the Central Pacific. The plan presented an opportunity to follow classic Japanese pre-war doctrine. The Japanese Naval Staff held back assets from operations in the Gilberts and Marshalls intentionally in preparation for another “decisive battle.”{163}
The Sixth (Submarine) Fleet plan for Operation A-Go had two major divisions. The first part consisted of specific submarines assigned solely to a combatant role. The second part of the plan comprised the submarines not specifically assigned that would be routed as available to handle any crises and react to American weaknesses and penetrations. In order to allow coordination between air, surface and subsurface assets and prevent fratricide of surface ships by the submarines, a demarcation line was established to the west of Saipan. Japanese submarines were not allowed to conduct attacks to the east of this line. The new overall strategic plan associated with Operation A-Go ensured that the submarines were still subordinated to operations other than strictly offensive or defensive. The primary tasking still revolved around fleet support.{164}
In preparation for the next American thrust, Takagi arrayed the thirteen available submarines in two major groups. Three were east of the Admiralty Islands while the other ten were north of the Admiralty Islands. The arrangement of the submarines presupposed that the next American move would be directly towards the Philippines. The available submarines included seven new RO-class medium submarines that lacked experience in combat. The crews had not had the opportunity to complete some operations in the Indian Ocean for experience prior to fighting in the Pacific.{165}
The submarines assigned to the scouting lines were again arrayed to fixed points in the ocean with little leeway for movement to patrol. Takagi conducted numerous communications with the submarines on the line. The rigid employment of the submarines and lack of concern for operational security with regard to communications led to the near destruction of an entire scouting line in May of 1944 by a single American destroyer escort (USS England).{166}
The debacle of the England affair started with the Japanese decoding of an American scout plane report. Surmising that the plane’s report was in reference to the position of RO-104, Takagi ordered a shift of the entire scouting line sixty miles from its original position. American intelligence assets decoded the orders from Takagi and provided the information to surface anti-submarine forces in the area.
Anti-submarine assets were dispatched to the area of the scouting line. On 22 May, three vessels started to overrun the line encountering submarines at thirty-mile intervals. RO-106 was sunk on 22 May. On the next day, RO-104 was sunk. Both submarines were sunk by the England. On 24 May, England sunk the RO-116 while failing to make contact with RO-105 which was occupying the spot between RO-104 and RO-116. England sank RO-108 on 26 May and after a few days of searching RO-105 was found and sunk on 31 May. Along with these five sinkings, England had also sunk the I-19 while it was conducting a supply operation on 19 May. England ended the war as the most successfully anti-submarine vessel of the entire war. With six sinkings, England was responsible for the majority of the nine Japanese submarine losses in May 1944.{167}
While the England fiasco was a significant loss for the Japanese submarine force, there were a small number of small positives in it. The Japanese were able to break some of the messages sent by the England after its first few successes and recognize the threat to the line. Orders to RO-109 and RO-112 had them vacate the line and survive the run by England. The disastrous loss of five boats from this line alone also saw the Japanese finally change their employment scheme to patrol areas vice scouting lines.{168}
The overly restrictive assignment of the few available submarines left them in poor positions to observe or influence the American offensive. The stationary patrol lines and poor attention to operational security left the Japanese submarines highly vulnerable to a concerted effort like that conducted by the England. The Sixth (Submarine) Fleet again failed to commit all available submarines to a major operation by continuing the ceaseless supply operations and other peripheral actions. The inconsiderate deployment of submarines cost the Sixth (Submarine) Fleet numerous submarines that were sorely needed prior to the major American attacks against the Marianas and the Philippines.
Based on the alignment of the aforementioned scouting line, the Japanese expected the next American thrust to be directed into the Philippine Sea from the south. As American airpower started to attack the islands of Saipan, Tinian, and Guam from the east, the Japanese believed the assault to merely be a feint and initially only committed 3 RO-class submarines to the area. In comparison, the American effort included 28 submarines for various duties. As the magnitude of the assault became apparent to the Japanese Naval Staff, all available submarines were rushed to the area.{169}
The movement of seventeen more submarines was conducted in a piecemeal fashion due to the disparate placement and status of Japanese assets. Submarines were shifted from lower priority efforts as well as being pulled out of refit and shipyard periods to be rushed to the battle. It took five days for the first submarine to arrive. After eight days, five more submarines were on station bringing the total force to nine. By the end of the tenth day, nineteen submarines were committed. The final submarine arrived on the eleventh day. The twenty submarines were deployed in a line positioned over 300 nautical miles east of the Marianas Island chain. This placement effectively put all of the submarines out of the fight. In the end, these twenty submarines had no sinkings during the course of the battle. The boats were unable to provide actionable intelligence or directly counter the American attack. Employment of the submarines was hampered by the attacks on Saipan which ultimately required the command of the Sixth (Submarine) Fleet to be temporarily transferred to the commander of Squadron 7 at Truk.{170}
Within two weeks of the deployment of all twenty submarines, nine would be sunk and most of the others would be pressed into supply and evacuation duties. Thirteen of the twenty would be lost by the end of the battles. As American pressure on Saipan grew, I-10 was tasked with evacuation Takagi and members of the Sixth (Submarine) Fleet staff. I-10 was sunk attempting the evacuation and I-38 was next to receive the same orders. After multiple attempts to retrieve the Admiral, I-38 was unable to safely avoid the American anti-submarine effort. Orders to continue to attempt the evacuation were cancelled. Admiral Takagi and his staff perished in the final banzai charge in defense of Saipan. I-41 had the lone successful act by a submarine during the attacks on the Marianas Islands. I-41 managed to evacuate 106 aviators from Guam making them available for further operations.{171}
The limited number of submarines used in the initial scouting lines coupled with their restrictive positioning kept the Japanese from being able to observe the movements of the American task forces. As such, insufficient submarines were positioned in the area where the Americans attacked. The disparate employment of available submarines significantly delayed the commitment of forces to stem the American invasion. Based on the singularity of the submarine force as a roadblock to the American advance, it is incomprehensible that anything less than the full complement of available submarines was made available to the effort. The secondary status of the submarine force still allowed assets to be drawn off by peripheral requirements and tasks regardless of the actual focus of the Sixth (Submarine) Fleet.
After the loss of the Marianas Islands, the Sixth (Submarine) Fleet sent submarines to attempt to interdict the transports and cargo ships sent with engineering forces and supplies to build facilities on Saipan, Tinian, and Guam. The patrols were ineffective at delaying the improvements on the islands. No ships were sunk and four submarines were lost in the attempts. Similarly, a number of patrols were sent to the large American anchorages at Ulithi and Peleliu. Again, no sinkings were registered by these efforts but two more submarines were lost.{172}
The staggering losses over the course of 1944 left the Japanese submarine force with 51 operational boats at the beginning of October after starting the year with 66. While the loss of fifteen submarines may not seem significant, the composition of the force changed dramatically. The number of large I-class submarines dropped to 28 from 42 while the smaller RO and HA-class submarines numbered only fifteen after starting the year at 24. The remaining eight submarines available at the beginning of October 1944 were supply submarines that were incapable of offensive or defensive operations due to their lack of torpedo tubes. The contraction of the submarine force left only fourteen submarines available to defend against the next major American thrust.{173}
As submarines were rushed to the vicinity of the Philippines, the Naval Staff pressed for as many radar-equipped submarines as possible to attempt to increase the effectiveness of the force. Fourteen submarines were available for defense of the Philippines from invasion. Much like the results in defense of the Marianas Islands, the submarine had little influence on the rate of American advance. Half of the submarines committed to the effort were lost. Three of these were sunk on a single day—23 October. Five days later another submarine was lost. The next loss occurred on 12 November, and it was followed by further sinkings on 18 and 19 November. Despite the continuous losses, the submarines continued to conduct attacks and they were able to have some very minor successes. The Japanese submarines recorded only one sinking: a destroyer escort. Three ships were damaged: an escort carrier (CVE), a tank landing ship (LST) and a light cruiser (CL).{174}
Ironically, the ineffectiveness of the Japanese submarines in the Marianas and Philippine Islands was indirectly caused by the success of American submarines. Japanese carrier airpower was severely limited in these battles due to prior losses and distant basing. The distant basing, in Tawi Tawi, was due to the success of the American submarines in interdicting oil shipments from Borneo. Basing in Tawi Tawi put the Japanese carriers close to the oil supplies in Borneo but kept them distant from the center of the American movements.{175}
The losses in the Philippines decreased the Japanese submarine force to a year-end strength of 51. While this is the same strength as at the beginning of October, the composition had changed dramatically again. The large I-class submarines had been whittled down to a year end strength of 21. The medium RO- and HA-class submarines accounted for sixteen of the total force. The supply submarines had grown to a total of fourteen to form the balance of the force.{176}
The large losses in June 1944 while fighting in the Marianas were the tipping point for the institution of drastic measures. The development, building and deployment of kaiten suicide torpedoes rose to a priority position. Almost all submarines, supply transports included, were modified for the purpose of carrying kaiten. Originally designed so that the operator could “eject” himself from the weapon prior to impact, the employment of these weapons was advanced with no intention of recovery of the pilots as Japanese losses and setbacks continued to mount. Kaiten-carrying submarines were formulated into the final defense plan as the first line of defense of the Home Islands. Having already started kamikaze attacks with aircraft, the step to suicide torpedoes was a short one.{177}
The move to kaiten use was not without merit when the overall state of the Japanese submarine force, and of the Pacific war, is taken into account. The Japanese submarine force had suffered heavy losses with little accomplished. Inexperienced crews were being sent to combat without the opportunity to conduct “warm-up” patrols in the Indian Ocean and other less challenging areas. The lack of resources was taking its toll on production capacity as material was expended on massive submarines that had little chance for influential operations. Small kaiten, kairyu and koryu submarines could be built en masse within the confines of the limited resources. The “guided” nature of these weapons also provided the opportunity to increase the effectiveness of Japanese attacks by focusing on key targets in a convoy or battle group.{178}
The first kaiten operation (Kikumizu) occurred in November 1944 by a force comprised of the I-36, I-37 and I-47 each carrying four kaiten. The target of the attack was the American anchorage at Ulithi and nearby passages. Of the twelve kaiten carried, only five were launched. I-47 launched all four at the anchorage while I-36 was only able to launch one due to mechanical issues. I-37 was sunk before being able to act. The returning commanders claimed the sinking of three aircraft carriers and two battleships for the five kaiten that were launched. The Navy staff reveled in the overwhelming success of the attack and promptly ordered further kaiten missions. Unfortunately, for the Japanese, the actual result of these attacks simply traded the lost I-37 for the sinking of a single American oiler (AO).{179}
Believing that the Kikumizu mission was highly successful, the second kaiten operation (Kongo) took place in January 1945 and consisted of six submarines each carrying four kaiten. The six submarines were assigned five separate targets including Ulithi and Guam. Mechanical issues and American ASW efforts impacted the total number of kaiten that were launched. Three submarines launched all four kaiten, one launched two, one failed to launch any while the final submarine was sunk and did not return. The Navy staff did assume however that all four kaiten were launched against the planned target before the submarine was sunk. Based on the “perfect” five sinking for five kaiten results of Kikumizu and optimistic reports from the returning submarine commanders, the Navy staff assumed eighteen sinkings for the eighteen kaiten employed. Postwar analysis indicated no sinkings as a result of the Kongo operation.{180}
A third kaiten mission (Chihaya) was hastily organized in February 1945 to attempt to repulse the American invasion of Iwo Jima. Three submarines were organized for this effort, two of which (I-368 and I-370) were supply submarines converted to carry kaiten. The operation continued the trend of poor results. No ships were sunk, and two submarines were lost. The third submarine was effectively frustrated by American anti-submarine efforts and was unable to launch any kaiten.{181} The tally at the end of three kaiten operations was four submarines lost for the sinking of a single American oiler. The Navy staff, however, was confident that every kaiten launched had sunk a ship and that the losses had bought the sinking of 23 American capital ships.
The next kaiten mission (Kamitake) was organized to replace the fruitless Chihaya operation. Two boats were assigned, but neither launched a kaiten. I-36 returned without result due to mechanical issues while I-58 had its orders cancelled. I-58 was subsequently ordered to operate as a radio beacon for a flying boat raid on Ulithi. The cancellation of orders and redirection of I-58 forced the boat to retrace its steps after having penetrated the anchorages near Iwo Jima. I-58 had actually manned its kaiten and was within an hour of engaging a number of targets when diverted. The subsequent air raid on Ulithi was ineffective at inflicting significant damage on the American Fleet and I-58 was ordered home with nothing to show for its patrol.{182}
The fifth kaiten operation (Tatara) was the first major attempt by the Japanese submarine force to influence the American invasion of Okinawa. Four submarines carrying twenty kaiten torpedoes were tasked in the operation. Two submarines, I-44 and I-56 were sunk while I-47 returned home due to excessive damage. I-58 was the sole submarine in the group not damaged or sunk. I-58 had been unable to close the anchorage due to heavy weather and American air patrols. I-58 had been tasked with joining a surface group, including the battleship Yamato, and conducting a coordinated attack. By the time I-58 was able to close range, the American carrier planes had decimated the surface group. I-58 would ultimately be ordered home without a victory or employing a single kaiten. Thus, Tatara ended with no sinkings for two losses.{183}
Up to this point, submarines carrying kaiten had been under strict orders to maintain radio silence until after their attacks were complete. The boats were also directed to forego torpedo attacks on other vessels before the assigned kaiten operations to avoid alerting American forces to the presence of submarines. Some commanders further interpreted their orders as requiring them to conduct no other attacks outside the kaiten operation. Thus, the significant desire for operational security to improve the chance of success for the kaitens limited the offensive capability of the submarines numerous times in this critical closing stage of the war. The submarines were relegated to a role as a transport for kaiten. This situation focused on the diminished experience of the submarine crews.{184}
In May 1945, VAdm Tadashigo Daigo took command of the Sixth (Submarine) Fleet. The focus of the submarine force and its kaiten operations was shifted away from the area of the invasion and the majority of the American combatants. American supply routes well behind the lines were the target. Along with the change in focus came a change in tactics. No longer would the submarines be constrained in their ability to attack outside of using kaiten. The kaiten were also targeted on moving ships at sea vice stationary ships in protected anchorages.{185}
The sixth kaiten operation (Tembu) involved two submarines carrying twelve total kaiten. I-36 launched four kaiten against convoys and reported four sinkings. Post war review of records shows no sinkings that match I-36’s kaiten attacks. I-47 attacked a convoy with four torpedoes for no sinkings. I-47 also attempted attacks with four kaiten the following day. Again there were no sinkings and only slight damage to a cargo ship. The two following kaiten operations (Shimbu and Todoroki) had five submarines carrying 23 kaiten. Ultimately, only four kaiten were launched for no sinkings. Two submarines were lost and a third was heavily damaged.{186}
The final kaiten operation (Tamon) involved six submarines carrying 35 kaiten. Only three of the submarines, with sixteen of the kaiten, would return to Japan. This would be the only kaiten operation, other than Kikumizu, that would result in a sinking.
The group would claim seven sinkings. The I-53 launched two kaiten to sink the American destroyer escort USS Underhill (DE). This would be the last vessel sunk by kaiten during the war. During the remainder of operation, a transport would be damaged off Okinawa and the Japanese would sink their last major American combatant. Both successes would use torpedoes instead of kaiten.{187}
The submarine I-58 departed Japan on 18 July 1945 carrying six kaiten in order to conduct attacks on shipping east of Philippines as part of the operation named Tamon. I-58 conducted numerous attacks during the patrol using both torpedoes and kaiten. Only one attack was successful. Observing a large warship one night, Commander Hashimoto chose to fire a salvo of six torpedoes instead of employing any of the kaiten that he carried. The choice to use the torpedoes was based on time of day and visibility. The victim of the attack was the American heavy cruiser USS Indianapolis at sea after delivering atomic bomb parts to Tinian.{188}
After nine kaiten operations to attempt to influence the American invasions of the Philippines, Iwo Jima, and Okinawa, the Japanese submarine force had very little tangible results. Eight submarines were lost during these operations while only managing to sink an oiler and a destroyer escort with kaiten. A small handful of other ships were also damaged. The kaiten were ineffective at generating more sinkings whether they were employed in anchorages or open ocean.{189}
The wholesale focus on kaiten employment as the final thrust of the submarine force to challenge the American offensive indicated the serious deficiencies that the submarine force was trying to overcome. The inexperience of replacement crews combined with the small number of submarines available for operations drove the use of kaiten. The strength of American forces combined with the haphazard and restrictive employment of the submarines confined them to limited results and numerous losses.
The Japanese submarine force found itself struggling to make the necessary impact as the American fleet drove through the South Pacific in to the Central Pacific. The submarine force found itself stretched as boats continued to be committed to areas well outside the focal point of the American operations. The submarines committed to the Indian Ocean and the Aleutian Islands drew vital assets away from the Pacific area of operations. The lack of assets was exacerbated by their restrictive employment and lack of concern for operational security. The submarine force was challenged in these circumstances to provide effective scouting and early warning without even considering actually conducting attacks.
The loss of submarines drove the Sixth (Submarine) Fleet staff to rearrange their method of employment of the submarines. Unfortunately, the decreased level of experience of the submarine crews late in the war was not conducive to the freedom of operation provided by using patrol areas. Previous lack of concern for operational security combined with inexperience in the more freely flowing operations away from scouting lines only combined to increase the number of losses without coincident increase in sinkings. While the overly restrictive scouting line alignment of forces negated the majority of the submarine’s unique capabilities, the shift to patrol areas failed to consider the lack of experience from both a submarine and staff standpoint. The shift came too late to build requisite knowledge and capitalize on the strengths of the submarines The rigid Japanese command and control system ensured that the submarines were unable to exercise the full breadth of their capabilities while it was in place, but further, it caused the force to not have the experience necessary to succeed in the decentralized environment..
Once the decision was made to employ kaiten was made, the submarine force finally decided to employ proper concern for operational security and subsequently hampered the effectiveness of the submarines sent out on successive operations. Even though the desire to protect the limited number of submarines that remained in operation was commendable, the staff failed to allow the submarines the freedom they needed in the initial kaiten operations to have an influence. The example of I-58 passing up numerous targets during Kamitake and Tatara and then scoring a victory during Tamon, once restrictions were removed, stands as a microcosm of the impact of the restrictive orders. Even with the change in weaponry, the ineffective method of controlling operations continued to influence the operational result.
For all of the positive changes that were ultimately made in the waning months of the war to ease the restrictions on submarines, the result had already been cast. The submarine force was too small to have an influence. The effectiveness was limited by the decreased capability as the percentage of transport submarines in the force rose. The resources devoted to transports and large submarines kept the faster Sen Taka Sho type submarines from reaching the fleet in numbers to return the advantage to submarines from the anti-submarine forces. The regular shifting of the submarine force’s strategic and operational focus kept the commanders in a state of confusion about how to conduct each successive patrol. The regular changes also challenged the staff to effectively deploy the submarines for maximum influence.