The number and characteristics of US and Japanese cruisers going into the Pacific War were determined by the series of treaties entered into by the major naval powers in the period between the wars. In 1921 the Americans proposed that a conference be convened in Washington with the purpose of limiting future naval construction. What resulted from the Washington Naval Conference was a Treaty for the Limitation of Armament signed on February 6, 1922. The focus of the treaty was on the numbers of battleships that each signatory nation could keep in service or build during the period the treaty was in effect. After existing ships were replaced, both the US and Britain were restricted to 500,000 tons of battleships and the Japanese 300,000 tons. The same tonnage ratio was established for aircraft carriers.
However, because of British objections, no similar restrictions were placed on the construction of cruisers. Nevertheless, all participants did agree that future cruiser construction could not exceed 10,000 tons per ship and that each ship could mount a maximum of 8-inch guns. This limit suited both the Americans and Japanese as it permitted the construction of larger cruisers, better suited for operations in the vast expanses of the Pacific. The unforeseen effect of the conference was to start a race to build more cruisers. With the construction of capital ships (battleships and battlecruisers) mostly eliminated, all major navies embarked on a program of building large cruisers. The treaty placed no limit on the number of these ships that could be built and the 10,000-ton cruiser quickly became the smallest of the future heavy cruiser designs being contemplated by both the Americans and Japanese.
After a failed attempt to place limitations on the overall tonnage of cruiser fleets during the Geneva Naval Conference of 1927, the major naval powers reconvened in January 1930 in London. By this time the British had relented on their insistence that they be permitted to possess greater cruiser tonnage than the Americans, so for the first time an agreement was reached limiting overall cruiser tonnage. As far as the US and Imperial navies were concerned, the First London Treaty allowed the following tonnage: Type A cruisers were defined as ships with guns greater than 6.1 inches (the 8-inch limit was still in effect), and Type B as those with guns of 6.1 inches or less. For Type A cruisers this constituted a limit of 18 heavy cruisers for the US Navy and 12 for the Imperial Navy. These limits were further defined during the Second London Naval Disarmament Conference held in 1935. By this point Japan had essentially withdrawn from the naval disarmament process, and the conference treaty was signed by the US, Britain, and France. It limited the construction of light cruisers to 8,000 tons, but the US had inserted a provision that this would not pertain to the 10,000-ton Brooklyn-class cruisers already under construction.
| Type A cruisers | Type B cruisers | Total | |
| US Navy | 180,000 | 143,500 | 323,500 |
| Imperial Navy | 108,400 | 100,450 | 208,850 |
Japan gave notice in 1936 she would withdraw from naval limitation treaties by the end of 1938. However for some 16 years the naval limitation treaties had defined the size and nature of the US and Japanese cruiser forces, and the resulting ships would form the backbone of their cruiser fleets in the coming war.
In December 1922 the US Navy building program called for 26 new cruisers – ten Omaha-class scout cruisers and 16 of the new 10,000-ton Treaty cruisers. Not until December 18, 1924 did Congress fund the first Treaty cruiser. At this time eight cruisers were authorized, but not fully funded until 1927. These were to become the two Pensacola- and the six Northampton-class ships.
The US Navy easily accepted the Washington Naval Treaty’s 10,000-ton, 8-inch-gun limit for its new cruisers. By 1920 the US Navy had already adopted designs for larger cruisers with 8-inch guns. The General Board, responsible for approving the designs of US Navy ships, foresaw several basic design requirements. As already mentioned, large cruisers would possess better range and seakeeping characteristics essential for Pacific operations. The primary mission of the Treaty cruisers remained scouting. In the era before radar, their range, speed, and comparatively heavy armament (useful for brushing aside enemy screening units) made them excellent scouting platforms. At the same time their heavy armament also made them suitable for missions that the more scarce battleships could not be risked for.
Preliminary designs for the first US Navy Treaty cruiser clearly showed a preference for firepower over protection. The ship was originally designed in 1923 to have 12 8-inch guns, a 35-knot maximum speed and only light protection (0.75 inches of armor over the magazines and 1.25 inches over the conning tower and steering gear). Concern over the lack of protection prompted the General Board to select a design in March 1925 that boasted only ten 8-inch guns and a speed of 32 knots, but which mounted some 1,090 tons of armor.
Design work for the Northampton class was already underway before the first ship of the Pensacola class had even been laid down. By reducing the number of main guns from ten to nine (mounted in three turrets instead of four), protection could be slightly enhanced and seagoing characteristics improved. Contrary to the expectations of their designers, the first two classes of US Navy Treaty cruisers came in well underweight. The Washington Naval Treaty defined limits in “standard” tonnage. This did not include the fuel and reserve feedwater, but did include stores. This complicated designers’ efforts to work up a balanced design within the 10,000-ton limit. In the case of the US Navy, fear of exceeding the limit led to excessive weight-saving measures, as evidenced by the final displacement of the first two cruiser designs. The Pensacola actually displaced 9,138 tons and the Northampton only 8,997 tons. The nature of these designs gave them excessive metacentric height that resulted in bad rolling in any kind of sea. Due to weight-saving measures, their construction was so light that the firing of all three turrets at once often caused structural damage.
The Pensacola and Northampton classes were quickly seen as inferior designs, largely for their relative lack of protection. Critics labeled them as “eggshells armed with hammers.” As soon as it was realized how much tonnage had been unused in these early designs, the US Navy was determined to do better with a second generation of Treaty cruiser.
After the completion of the first eight Treaty cruisers, in 1929 the US Navy proposed another 15 ships to be built in groups of five. The first group was ordered as an improved version of the Northampton class. The principal difference in these ships was a higher standard of armored protection; for example, the side armor protecting the magazines was to be increased from 4.25 inches to 5.75 inches. One ship was to be fitted out as an alternate fleet flagship.
Design work for the second group of five cruisers was also well underway. It was obvious that this was superior to the improved Northampton design, so the US Navy decided to retroactively use the superior design on the first group of cruisers. However two ships had already been awarded to private yards and the cost of changing the designs would have been too high. These two ships became the Portland class. The other three ships of the first group (New Orleans, Astoria, and Minneapolis) were built to the improved design, becoming known as the New Orleans class.
Completion of the entire second group of five ships was curtailed by the London Naval Conference, and only four were completed – Tuscaloosa, San Francisco, Quincy, and Vincennes. All these were modified to some extent. Most modifications involved slight redesigns to incorporate weight-saving measures, since after the earlier tendency of American designers to produce underweight designs, they now tended to the other extreme with the second-generation Treaty cruiser design. None of the New Orleans-class ships were designed with torpedo tubes, unlike earlier Treaty cruiser classes. The New Orleans class also introduced armored turrets rather than the gunhouses of the earlier ships.
A 1940 view of Quincy shows the layout of the US Navy’s last Treaty heavy cruiser design. As opposed to earlier classes, this New Orleans-class cruiser has improved 8-inch turrets, a reworked bridge, pole masts in place of the previous tripod masts and a different placement of the ship’s aviation facilities and 5-inch secondary battery. The markings on her turret tops are for aerial identification. (US Naval Historical Center)
The London Treaty forced a new direction for American cruiser design. The construction of 8-inch cruisers was capped after the completion of the last New Orleans-class ship and the final 8-inch cruiser, the unique Wichita. The new 6-inch-gun cruisers, known as the Brooklyn class, introduced several new features. The aviation support facilities were moved aft, unlike on every other Treaty cruiser class where they were placed amidships. The new 6-inch gun used semifixed ammunition that permitted a high rate of fire. American designers hoped that the volume of fire possible with the 6-inch gun would compensate for the heavier shell used by the 8-inch cruisers. Originally the Brooklyn class was to carry 12 6-inch guns in triple turrets, but when the Japanese announced in January 1933 that the new Mogami-class light cruisers would carry 15 6.1-inch guns, the early Brooklyn design was recast to match the Japanese. The design of these ships was predicated upon providing speed and radius equal to that of the 8-inch-gun cruisers. It was intended that these ships would also possess sufficient armor to withstand 8-inch gunfire. In 1934 the first three 10,000-ton light cruisers were authorized by Congress, after much deliberation on the merits of a smaller design that would permit more ships to be built with the US Navy’s remaining cruiser tonnage. In the end it was decided not to accept the firepower and protection limitations of a smaller (8,000-ton) design. Seven ships were eventually built to the Brooklyn design.
The last two ships of the Brooklyn class were completed to a modified design and became the St Louis class. The principal difference was the desire to replace the 5-inch/25 gun with the demonstrably superior 5-inch/38 gun. Instead of the single mounts on the Brooklyns, the last two ships featured the first twin dual-purpose 5-inch gun mounts placed on a cruiser. Four were fitted, providing the same secondary armament as the eight single 5-inch mounts found on the Brooklyns. The St Louis class also featured superior internal arrangements, with the separation of the two engine rooms from the two boiler rooms providing a better ability to withstand battle damage.
The last of the Treaty cruisers was a Brooklyn-class ship modified to carry 8-inch guns. The London Naval Treaty of 1930 allowed the US Navy to lay down an 8-inch cruiser in 1934 and 1935. The first ship was the last unit of the New Orleans class, but the last heavy cruiser laid down was a hybrid. By using the hull of the Brooklyns, steaming radius would be increased and the superior arrangement for the aviation facilities and secondary armament could be adopted. Wichita became the design departure point for the very successful Baltimore class of war-built heavy cruisers.
Between the wars, the US Navy worked intensively to develop a doctrine that combined aggression with effective control and coordination of all types of fleet weapons to quickly overwhelm and defeat an enemy. The view commonly held by the Navy’s leadership was that the coming war would be against Japan and that a decisive battle with the Japanese fleet would be fought somewhere in the western Pacific. This was driven by the US Navy’s adherence to the Mahanian view of decisive victory.
In this great set-piece naval engagement, the cruiser force had important roles to play. Cruisers were charged with screening more vulnerable units of the American fleet as the two navies advanced into action. More importantly, cruisers were ideal platforms for performing the scouting mission. They possessed sufficient endurance to operate independently and had the firepower to brush aside enemy screening units to determine the enemy’s strength and movement. During the decisive action, most cruisers would operate in the vanguard of the fleet. Destroyers would be used aggressively to attack the enemy fleet, and cruisers would provide fire support to clear a path for the destroyers, but they would keep their distance from enemy units to avoid torpedo attack. During the inevitable exchange of gunfire between the two main fleets, cruisers would also engage enemy battleships and battlecruisers.
While these efforts may have been useful in a major fleet engagement that never happened, they proved utterly inadequate at Guadalcanal. The focus on so-called “major tactics” at the expense of “minor tactics” (engagements between single ships or small groups of ships) would prove very costly.
Night warfare was not ignored by the US Navy, but it was not seen as the decisive phase of combat. Going into the Pacific War, the US Navy assumed that night combat would be decided by the swift application of accurate gunfire. Torpedo tactics were stressed, but were not applicable to the situation that emerged at Guadalcanal. Every exercise stressed the importance of quickly finding the range, and fire-control procedures had been streamlined in the interwar period. During night combat it would be even more critical to score hits quickly as actions would be fought at shorter ranges. To achieve this, the US Navy developed the tactic of opening fire quickly, even before adequate illumination, and then using the splashes of the shells to determine range. Once the range had been established, a tactic of “rocking” salvos back and forth over the target addressed the unsolvable problem of ascertaining how many shells were actually hitting a target at night. For highly trained crews, this proved an effective tactic. Cruisers of the Brooklyn class, with their faster-firing 6-inch guns, were able to smother a target using this tactic. With the advent of radar with sufficient accuracy to allow for radar-guided gunnery, the range was found even earlier and gunfire was more deadly.
Four units of the Pacific Fleet’s Scouting Force shown in 1933 maneuvering together to land floatplanes. Scouting was viewed as a primary heavy cruiser mission during a major engagement with the Japanese fleet. (US Naval Historical Center)
The design of the first Japanese heavy cruisers actually pre-dated the Washington Naval Treaty. However, they were destined to play prominent roles in the Pacific War and influenced subsequent classes of Japanese cruisers. Their genesis was a desire to produce a ship superior to the US Navy’s Omaha class and the Royal Navy’s Hawkins class. To do this, the Japanese settled on a 7,500-ton design with six 7.9-inch/50 guns and a 35-knot speed. Because these ships were under the 10,000-ton Washington Naval Treaty limit, their design was not affected when the treaty was signed in February 1922.
The Imperial Navy actually completed four heavy cruisers to pre-Treaty designs. These included two ships of the Furutaka class and two Aoba-class units. Furutaka set the tone for future Japanese cruiser construction, with the design featuring a heavy armament on a fairly small hull and, importantly, the provision of a large torpedo battery. Protection was clearly secondary to firepower. Speed was also emphasized.
Kako shown shortly after her completion in 1926. The ship is in her original configuration with single 7.9-inch gunhouses and fixed torpedo tubes. The three sets of fixed starboard torpedo tubes can be made out just forward of the bridge and aft of the second stack. (Yamato Museum)
As soon as the Washington Naval Treaty had been signed, the Imperial Navy began design work on its first true class of Treaty cruisers. Like the US Navy, the Japanese quickly decided that it made no sense not to build to the full 10,000-ton limit and give the ship 8-inch guns. The original design specifications of the class called for eight 8-inch guns fitted in four turrets (three forward and one aft), four 4.7-inch guns, and eight 610mm torpedoes fitted in four twin mountings. Speed was to 35.5 knots and range was 10,000nm at 13.5 knots. Armor was not neglected and was to provide protection from indirect fire from 8-inch guns and for critical areas from direct 6-inch fire. As the design was approved in August 1923, it included an increase to ten 8-inch guns, deletion of the torpedo tubes, and a reduced cruising range. Of note, the approved design met the 10,000 limit of the Washington Naval Treaty.
However, as built, the Imperial Navy’s Myoko class of Treaty cruiser was different. The Navy General Staff was persuaded to bring back torpedo tubes on the ship and change the twin tubes to triple tubes. Another addition brought the number of 4.7-inch guns up to six. These changes and others would clearly bring the ship to over 10,000 tons; when the first ship ran trials, its standard displacement was 11,250 tons. This violation of the Treaty limits was willful on the part of the Japanese and was, of course, not reported.
To keep pace with the US Navy, four additional heavy cruisers were approved under the 1927 Reinforcement Program. This was to become the Takao class and would be the Imperial Navy’s most powerful class of Treaty heavy cruisers. Originally these were to be follow-on Myoko units, but the Imperial Navy decided it could improve the design. Principal improvements included increasing the elevation of the 8-inch battery to over 70 degrees to allow their use in an antiaircraft role. This would permit the number of 4.7-inch guns to be reduced to four. Armor protection was also increased, particularly around the magazines. Other improvements included fitting two catapults and the exchange of the fixed torpedo mounts for trainable triple mounts. These were mounted on outboard sponsons with the idea that if they ever exploded, the loss of the entire ship could be prevented.
Myoko in the configuration in which she would go to war. Her main battery is now 8-inch guns and the 4.7-inch guns have been replaced by twin 5-inch guns. Aft of the second stack, she has been fitted with a raised flight deck with two catapults. The heavy torpedo battery of four quadruple mounts is fitted under the flight deck. (Yamato Museum)
The Takao-class cruisers shared a similar hull line with their predecessors, but their appearance was dramatically altered with the inclusion of a large forward superstructure. This large bridge structure reflected the requirement that Takao-class ships be fitted as flagships; their superstructures had three times the internal volume of those of the Myoko class. They also increased speculation that the Japanese were exceeding cruiser Treaty limitations. The Japanese were aware that the improvements on the class would add more weight and to compensate they made extensive use of welding – rather than riveting – during construction. Nevertheless the ships exceeded their design displacement by over 10 percent, for a total of 11,350 tons. Ever since the Furutaka class, the Imperial Navy had consistently used incorrect design calculations. This practice, never corrected, constituted willful evasion of Treaty limitations.
A fine study of Ashigara following her 1935 modernization. Note the position of the two quadruple torpedo tubes in their port-side sponsons. This placement was an attempt to mitigate damage if the torpedoes exploded. (Yamato Museum)
The completion of the four Takao-class units gave the Imperial Navy 12 heavy cruisers – their limit under the London Naval Treaty. Under the treaty, the Japanese still possessed a small amount of tonnage for Type B cruisers. This was combined with a treaty provision that aged ships could be replaced to free up tonnage for a new class of four light cruisers that was to be begun in 1931 and completed by 1937. Work on the new design began in 1930 and, as usual, Japanese designers were tasked with an impossible set of design requirements to be met within a set tonnage limit. The ships were limited to 8,500 tons but were to be armored as well as a heavy cruiser, and still mount a heavy armament of 15 6.1-inch guns and 12 24-inch torpedo tubes. One of the design principles for this class was that the 6-inch battery would be replaced by 8-inch guns as soon as conditions permitted.
To do this, every possible measure to reduce weight was incorporated into the design. In spite of this, design displacement in 1931 was 9,500 tons and stability was dangerously compromised. Concerns about the stability of the design were increased when in March 1934 a torpedo boat capsized in heavy seas and again a year later, when several ships were damaged in a typhoon. In response to the 1934 incident, the design had already been modified for the first two ships, but this did little to ease the stability problems. After the typhoon incident, the entire class was returned to the shipyards for major reconstruction. By January 1938, work on all four ships was completed. This was followed by a 1939 refit for the entire class, which replaced the triple 6.1-inch turrets with twin 8-inch turrets. What finally emerged by the start of the Pacific War was a ship with capabilities similar to the previous classes of heavy cruisers. The Mogami class now carried ten 8-inch guns, a secondary battery of eight 5-inch guns mounted in twin gun mounts, and a heavy torpedo armament with reloads. Protection was on the same scale as previous classes of Imperial Navy heavy cruisers.
Takao following her completion in 1932. The similarity to the Myoko class in overall layout and hull design is obvious, with the salient exception of the massive bridge structure. (Yamato Museum)
Suzuya as originally completed. This view shows the layout of her main battery (still 6-inch guns during this period), which employed a unique superfiring position for Turret 3. The position of the torpedo battery has been moved aft as on the Myoko class. (Yamato Museum)
The final class of Japanese heavy cruisers was laid down in 1934 and completed in 1938–9. This was the two-ship Tone class, which was originally to be similar to the Mogami class. However, with the mounting problems related to the Mogami design, the Tone class was recast on an entirely different basis. As reinvented, the Tone class would be designed as a heavy cruiser with extensive aircraft-carrying capabilities. This required the main battery to be situated on the forward part of the ship allowing the aft portion to be devoted entirely to aircraft operations. A heavy torpedo armament was still fitted. During the war these ships operated as part of the Imperial Navy’s carrier forces; not until late in the war would these ships operate in a dedicated antisurface role.
This view of Chikuma shows the unique configuration of the Tone-class cruisers. All four 8-inch turrets are placed forward with the aft portion of the ship dedicated to the operation of as many as five aircraft. (US Naval Historical Center)
Like the US Navy, the Imperial Navy was convinced that the big guns aboard the battleship would be the final arbiter of naval warfare. However, even given this important similarity, the Japanese had developed a very different scheme for employing their cruiser force.
Unlike the US Navy, Imperial Navy cruiser tactics revolved around the use of the torpedo. After the big battleship gun, the torpedo was the Imperial Navy’s weapon of choice. Because a torpedo platform had to approach fairly close to its target to be most effective, torpedoes were seen as most useful in a night engagement. However the Imperial Navy spent considerable resources developing a long-range torpedo that could be used day or night. The solution was an oxygen-propelled torpedo that came into widespread service in 1936. This was the Type 93 torpedo, known eventually to the US Navy as the Long Lance. The first ships to receive these top-secret weapons were the heavy cruisers. Tactics for the new torpedo called for the heavy cruisers to fire them in large numbers at extended ranges – day or night – before the enemy was even aware that he was in danger. With the enemy in confusion following the torpedo damage, destroyers would execute further torpedo attacks at closer ranges. This led to intense Japanese rehearsal of torpedo tactics, including large-scale firings day and night, and constant attention to reducing torpedo reloading times. Given their torpedo superiority, the Imperial Navy believed it would have the advantage in any cruiser engagements.
The four units of the Takao class, all shown here with a number of light cruisers, formed the 4th Cruiser Squadron. These powerful ships were an important part of the Imperial Navy’s intricate plans for a decisive naval engagement with the US Navy. (Yamato Museum)
Night combat was always a central feature of the Imperial Navy’s strategy as well as its war-fighting doctrine. Because of its numerical inferiority to the US Navy, the Imperial Navy viewed night combat as an opportunity to inflict attrition on the US battle line and prepare it for defeat at the hands of its own battle line.
To conduct night combat, the Japanese possessed several important tools. Conventional night-fighting tactics relied on the use of large ship-mounted searchlights to provide illumination of targets. However this also provided the enemy with an aiming point, so star shells and parachute-deployed star shells were also developed. Probably the biggest advantage the Japanese possessed at night were the superior optics that often provided vision out to ranges equal to or superior to early American radar. For night combat, each destroyer flotilla was supported by a division of heavy cruisers, together becoming a “night combat group.” The cruisers would employ their torpedoes at maximum range and provide gunfire support, allowing the destroyers to penetrate enemy formations.