The seizure of the Marshall Islands in the Central Pacific had long been recognized as a necessity in a war with Japan. As far back as 1921, Marine Major E.H. “Pete” Ellis had formatted a hypothetical plan to seize four Marshall’s atolls to serve as staging bases for further naval operations against Japan. Ellis died under mysterious circumstances in the Japanese-controlled Palau Islands in 1923.
In May 1943 the “Trident”, or Washington, Conference determined the war’s course and reexamined earlier decisions. In regards to the war with Japan, two thrusts would converge on the Home Islands. The main effort would be in the Central Pacific by Admiral Chester Nimitz’s Pacific Fleet, with General Douglas MacArthur conducting a secondary effort in the Southwest Pacific through New Guinea and the Philippines. MacArthur argued for a concentration of effort in the Southwest Pacific, but it was felt the Japanese would mass their forces to meet one thrust. The Central Pacific route was more direct and required fewer troops. The Japanese would be unable to deploy as many troops and aircraft on the small widely scattered islands as they could in New Guinea and the Philippines. The Gilberts and Marshalls were earmarked to be seized.
US Fifth Fleet seized the Gilberts after the bloody November 1943 battles for Tarawa and Makin. Meanwhile, US and Australian forces were advancing in New Guinea. A major issue was to decide which atolls in the Marshalls would be seized. The Japanese had bases on six atolls plus Kusaie and Wake Islands. On 1 September 1943, Eniwetok Atoll (the northernmost), Kusaie Island (westernmost), and Wake Island (far to the northeast, but under control of the Japanese Marshalls forces) had been selected as targets to be taken. At this time the new 4th Marine Division (MarDiv), 7th Infantry Division (InfDiv), and the separate 22nd Marines were designated to execute Operation “Flintlock” (originally “Bankrate”) under the command of the Marine V Amphibious Corps (VAC). However, Admiral Nimitz proposed Kwajalein (the main base near the Marshalls’ geographic center), Maloelap, and Wotje (the latter two being closer to Pearl Harbor) as alternatives. These three atolls held 65 per cent of the air bases in the Marshalls and the other bases could be neutralized without necessarily being physically occupied. The target date was 1 January 1944. The date for the seizure of Eniwetok by 27th InfDiv was tentatively set as 1 May, however, when it became clear that the atoll was lightly defended, the assault was rescheduled for 1 March.
A pre-bombardment view of Namur Island. This is the Yokohama Pier on the island’s south-central coast, the lagoon side. The pier would serve as a boundary between the two landing beaches and the two assault battalions. In the upper left corner can be seen the concrete causeway connecting Namur to Roi.
By the time of the invasion Namur’s appearance had been transformed by extremely heavy naval and aerial bombardment. This view is looking south across the island into the lagoon. While devastating the island’s facilities, the bombardment created obstacles to movement because of the downed trees, wreckage, and craters. It also provided hiding places for the defenders. The torpedo warehouse’s crater can be seen below the “V” of the three large concrete structures near the left edge.
Initial planning was conducted prior to the Tarawa assault but lessons from this operation were subsequently incorporated. Earlier amphibious landings had been mostly conducted against large hilly and forested islands against limited or no resistance. The lessons learned in the Tarawa assault, a small atoll island ringed with strong defenses, were critical: particularly those pertaining to using amphibian tractors to attack across broad coral reefs. This was the first assault in which amphibian tractors (“amtrac”, landing vehicle, tracked – LVT) were employed to deliver assault troops. They were previously used as cargo carriers. Other lessons were also learned, especially with regard to naval gunfire and aerial bombardment. Based on the experiences at Tarawa, it was realized the forces available for “Flintlock” might not be able to secure the proposed objectives. Operational planning was reevaluated, changes made, and less ambitious objectives assigned. On 7 December, Kwajalein became the primary objective and D-Day was set for 17 January. The revised plan, designated “Flintlock II”, was issued on 20 December. Admiral Raymond A. Spruance, Commander, Central Pacific Forces and Fifth Fleet, expressed concerns that Kwajalein was located deep within the Japanese defenses, preferring Wotje and Maloelap to be secured first. Nimitz soon recommended the target date be changed to 31 January. The Joint Chiefs of Staff insisted the operation commence in January, but the landing forces could not be ready by the original 17 January date. Admiral Spruance, still concerned about bypassing the outer bases, requested that Majuro Atoll to the east be secured. It was either lightly or undefended and would provide airfields to protect Kwajalein from Japanese forces on Jaluit, Maloelap, Wotje, and Mille. It would also serve as a fleet anchorage. The 106th Infantry was assigned to the operation and a reinforced battalion tasked to secure Majuro. A further delay was requested, to 10 February, to allow the divisions to fill equipment shortages and permit the 4th MarDiv to conduct a full rehearsal. This request was denied.
The other bases were to be neutralized by air and naval bombardment through the campaign. Eniwetok in the extreme northeast of the Marshalls would receive particular attention, as it was key to the aerial supply route from Japan. It would be seized later in the operation to block this flow. Once the objectives were secured they would be developed to provide staging and supporting bases for the Western Pacific drive. The bypassed islands would continue to be neutralized from the new American bases established on the captured atolls.
A Japanese expeditionary force took control of the German possessions of the Marshall, Caroline, and Mariana Islands in 1914. In 1920 Japan was granted a mandate by the League of Nations to govern the islands, effective 1922. To garrison and defend the Japanese Mandated Territories, or simply the Japanese Mandate, the South Seas Defense Force was formed. The civilian-run South Seas Bureau, operating under the Ministry of Overseas Affairs, was headquartered on Koror in the Palau Islands, Western Carolines.
By the late 1930s, Japanese settlers outnumbered the native Micro-nesians, or Kanakas, as they developed the islands economically. After serving the required two-year notice, Japan withdrew from the League of Nations in 1935 and the Mandate became a “closed territory” with entry by Westerners restricted. Japan was accused of illegally fortifying the islands, but was under no legal obligation not to do so.
In November 1939, Japan activated the 4th Fleet to defend the Mandate with amphibious and light forces. Each of the three main island groups was provided with an independent defense system centered on Jaluit, Truk (pronounced “Chuck”), and Saipan. The defense strategy was to marshal, service, and supply 4th Fleet air and naval forces as they launched raids and small-scale operations out of range of enemy bases and reconnaissance aircraft. This would buy time for the Combined Fleet to deploy to meet the invading fleet and defeat it in a decisive engagement.
The Mandated Territory totaled some 1,458 islands, islets, and reefs; 860 square miles of land in total. They spanned an area of 2,500 miles (4,023km) from east to west and 1,200 miles (1,931km) north to south. The Marshalls are the easternmost group and lie north of the Gilberts and the Equator. The Carolines are strung out to the west running toward the Philippines while the Marianas are to the north of the central Carolines.
Militarily the Mandate provided Japan with a barrier to the Australian, British, American, and French possessions to the south and east, an outer defense belt, but they could also serve as a launch point for the conquest of those same territories.
The Marshall Islands (US codename “Bully”), or Maasyaru Shoto to the Japanese, are roughly 2,500 miles (4,023km) southwest of Hawaii, 2,500 miles southeast of Japan, and 1,000 miles (1,609km) northeast of New Guinea. The Eastern Caroline Islands are some 500 miles (805km) to the west, with the great Japanese naval base at Truk some 900 miles (1,448km) and Guam 1,500 miles (2,414km) in the same direction. The Gilberts are 160 miles (257km) to the southeast. The Marshalls contain 29 atolls, five separate islands, and 867 reefs providing only 70 square miles of land and scattered over 750,000 square miles of ocean. Counting the atoll’s islets there are 1,152 islands. The islands are arranged in two parallel chains running northwest to southeast, separated by roughly 100 miles, the eastern Radak (Sunrise) Group with 16 atolls and islands and the western Ralik (Sunset) Group with 18 atolls and islands.
Atoll codenames
Only the codenames of the key atolls on which action occurred or on which major Japanese installations were situated are listed.
| Common Name | Codename |
| Kwajalein | “Porcelain” |
| Majuro | “Sundance” |
| Eniwetok | “Downside” |
| Jaluit | “Deadwood” |
| Maloelap | “Cordial” |
| Wotje | “Creosote” |
| Mille | “Caddie” |
Spain discovered the first of the Marshalls in 1525 and annexed the islands in 1686, but little effort was made to develop them. In the late 1700s and early 1800s various Russian, British, and American explorers discovered more islands. They were named after British Captain John Marshall, who discovered some of the southern Radak Group. There was no government within the islands and freebooters, adventurers, and traders did as they pleased. Germany purchased the islands from Spain in 1899 and annexed them in 1902.
From 1914 Japanese trading firms took over control of the islands and the previous Australian interests dwindled. The first simple airstrip to be built in the Marshalls was laid out on Roi in the mid-1930s. The only available pre-war population figures date from 1935, listing 10,000 native Marshallese and 490 Japanese. The islands experience a northeast trade wind from December to May, a dry season with little rain. From June to November the southwest monsoon brings 5–15ins. (12.7–38cm) a month. Temperatures range from the high 60°Fs at night to the high 90°Fs in the day and humidity can be high. Rain catchments are the only source of freshwater.
Kwajalein Atoll
Kwajalein Atoll island codenames
Only the codenames of the islands on which action occurred are listed. Common names will be used for the main islands, but codenames are used for smaller outlying islands as the native names were confusingly similar or the smaller islets had no common name. Interestingly, today some of the islets are more commonly known by their wartime codename rather than their traditional name.
| Common Name | Codename |
| Northern Kwajalein | |
| Roi | “Burlesque” |
| Namur | “Camouflage” |
| Ennuebing | “Jacob” |
| Mellu | “Ivan” |
| Ennugarret | “Abraham” |
| No name | “Albert Junior” |
| Ennumennet | “Albert” |
| No name | “Alexander” |
| Ennubirr | “Allen” |
| No name | “Alton” |
| No name | “Alvin” |
| Obella | “Andrew” |
| No name | “Anthony” |
| Edgigen | “Anton” |
| Southern Kwajalein | |
| Kwajalein Island | “Porcelain” |
| Ebeye | “Burton” |
| Enubuj | “Carlson” |
| Ennylabegan | “Carlos” |
| Gea | “Carter” |
| Ninni | “Cecil” |
| Gehn | “Chauncey” |
Most of the Marshalls’ land area consists of coral atolls varying 3–20ft (0.9–6.1m) above sea level with around 7ft (2.1m) being the average. The larger islands are covered with coconut palms, pandanus and breadfruit trees, and salt brush. The smaller ones are bare or covered with salt brush. All atolls and islands are surrounded by coral reefs, which lie closer to shore on the lagoon side. The beaches are narrow and either flat or very gently sloping.
Atolls are the lips of subsided volcanoes on which coral has formed over millions of years to create a large roughly circular reef. Most of the reef is beneath the surface, but numerous islets have built up along the lip. Gaps of various widths allow entry into the reef-enclosed lagoon, which provides a protected anchorage. The Japanese physically occupied few of a given atoll’s islets, usually only those large enough for an airfield and support facilities. Often the largest island of an atoll bore the atoll’s name.
Kwajalein (pronounced “Kwa-dja-linn”) Atoll measures 66 miles (106km) in length and is 20 miles (32km) across. There are 93 islands and islets with 38 being of significant size. Despite being the world’s largest atoll, its total land area is still only 6⅓ square miles. Kwajalein forms a misshapen triangle with numerous breaks in the reef allowing entry into the lagoon. The atoll forms two arms to the south and the west, with a small portion projecting to the north.
Conjoined Roi and Namur Islands are at the corner of the northward-projecting barrier reef, the atoll’s northernmost islands. Both islands are irregularly shaped and separated by 500yds, but connected by a sandspit along the lagoon side and a concrete causeway. Roi measures 1,170x1,250yds (1,070x1,143m) while Namur is 800x890yds (732x812m). Both islands had well-developed road systems. An airfield (shaped like a number “4”), taxiways, and dispersal areas occupied most of Roi, with a few hangars and machine shops. Airfield support facilities, machine shops, and barracks were concentrated on Namur. The L-shaped 450ft-long (137m) Yokohama Pier jutted into the lagoon from Namur while a much shorter pier was located on Roi. Both islands are low and flat. On the ocean side the reef is 125–450yds (114–412m) broad and falls steeply into the sea resulting in heavy surf. On the lagoon side the reef is gradually sloped with light surf. A line of small islands and islets runs southeast from Namur along the barrier reef. The largest and closest are “Abraham” (460yds/421m away), “Albert”, “Allen”, and “Andrew”. Two miles (3.2km) to the southwest of Roi is “Jacob” on the edge of “Jacob Pass” and 2 miles farther on sits the somewhat larger “Ivan” beside the main entrance into the lagoon, “Ivan Pass”.
Kwajalein Island is crescent-shaped with its concave side on the lagoon or north side. It is two and a half miles long and averages 800yds (731m) wide, but narrows to 300yds (274m) at the north end. Kwajalein Island is located at the extreme south end of the atoll. Kwajalein’s beaches slope steeply to 10ft above sea level. In 1944 both Kwajalein and its adjacent islands were covered with woods, these being densest at the north end. A road ran around the island of Kwajalein, and two 100yd-long (91m) wharves and an L-shaped, 500yd-long (457m) one jutted into the lagoon. Numerous administrative buildings, barracks, machine shops, and warehouses were built along the north shore and toward the north end. A large building complex was located inland where the island ran north and was known as the Admiralty Area – the island headquarters. A radio direction-finder was located near the west end. Most of the Japanese defenses were positioned along the ocean side and the north and west ends. The uncompleted 5,000ft (1,524m) airfield was located in the central section of the island. On the lagoon side the reef is 500–800yds (457–731m) wide and studded with boulders and outcrops. On all sides, the beaches are 10–20yds (9–18m) wide, rising to higher ground. “Carlson” Island is three miles (4.8km) northwest of Kwajalein and is two-thirds of a mile long and less than 300yds (274m) wide. Some 4,300yds (3,932m) northwest of “Carlson” is “Carlos”, one mile long and 300yds wide. Two islets are located nine miles northwest of Kwajalein and a half-mile beyond “Carlos” – “Carter” and “Cecil”. The two sit on either side of the half-mile-wide “Cecil Pass” through which the attack force would enter the lagoon.
The results of the 18–19 November 1943 carrier strike on Mili Island, the main island in Mille Atoll. This atoll was one of the by-passed Marshalls, which remained in Japanese hands to the end of the war. Part of the airfield can be seen in the upper right.
The third most strongly defended island in the atoll was Ebeye, or “Burton”, located two and a half miles north of Kwajalein Island. The rectangular-shaped island is 1,770yds (1,619m) long north to south and 250yds (229m) wide. Engebi was dotted with palms and brush with the densest brush and mangroves on the ocean side of the island. An improved road ran along the lagoon side and an L-shaped pier jutted 530yds (485m) into the lagoon. Two seaplane ramps occupied the northern portion of the lagoon side. As well as a radio direction-finder, there were some 250 barracks, support buildings, hangars, and machine shops scattered over the island.
Majuro is in the lower portion of the eastern Radak Group 280 miles (451km) southeast of Kwajalein. Arno Atoll is nine miles (14.5km) to the east. Elongated Majuro is 26 miles (42km) east to west and six miles (9.7km) wide. Most of its circumference is edged with a continuous reef with the only openings on the north-central side. Majuro Island (“Laura”) is the largest of the atoll’s 57 islets. It is a narrow sandbar, no more than 300yds (274m) wide and 21 miles (33.8km) long, running east from the atoll’s southwest corner, where a 1x1¾-mile-wide lobe sits. Sandbar islets are scattered along the south side for some 12 miles (19km). At the tapered east end are three larger islets, and more islets are scattered along the north side. The submarine reef continues northwest to a few islets on the atoll’s northwest corner. The 33 islands and islets are covered with low salt brush. The Japanese built a seaplane base on Darrit Island at the atoll’s northeast corner.
Eniwetok island codenames
Only the codenames of the islands on which action occurred are listed.
| Common Name | Codename |
| Engebi | “Fragile” |
| Eniwetok | “Privilege” |
| Parry | “Heartstrings” |
| Bogon | “Zinnia” |
| Aitsu | “Camellia” |
| Rujiyour | “Canna” |
| Japtan | “Ladyslipper” |
Eniwetok (pronounced “En-ni-we-tok,” vowels short, no accent), the northwesternmost atoll in the western Ralik Group, is 337 miles (543km) northwest of Kwajalein. It served as an outpost for Truk some 400 miles (644km) to the southwest. The roughly circular atoll has 40 islets and is 21 miles (34km) across from northwest to southeast and 17 miles (27.4km) across the center. The highest elevation is 15ft (4.6m). On the south side of the atoll is the Wide Passage, five-miles wide, which is the main entrance into a lagoon providing anchorage for up to 2,000 ships. Eniwetok Island is the largest in the atoll and is on the east side of Wide Passage. It was commonly known as Brown Island and to the Japanese as Chairo Jima. Parry Island, the third largest, is two and a quarter miles to the northeast of Eniwetok Island with the one-mile-wide Deep Passage off its north end. On the north side of Deep Passage is Japtan Island. On the atoll’s northeast side is a string of scattered islets with Engebi Island, the second largest, at the north end.
Taroa Island in Maloelap Atoll was another island that remained under Japanese control. This photo was taken early in the bombing campaign to neutralize the island. By the time the war was over its surface was more akin to that of the Moon. Aircraft revetments are scattered near the apex of the X-shaped airfield.
Carrier aircraft attack Japanese shipping moored off Kwajalein Island. Most of the ships were sunk during this attack. The 500yd-long (457m) concrete pier near the island’s north end juts into the lagoon.
Prior to the war the Japanese had established no military facilities in Eniwetok Atoll. It was not until December 1942 that work began on an airfield on Engebi, which was completed in mid-1943. The airfield was not used until November, when it became a ferrying way-station for aircraft withdrawing westward into the Carolines.
Engebi Island is a low and flat triangular island measuring 1,500yds (1,371m) on its northwest side, 2,000yds (1,829m) on its east, and 2,100yds (1,920m) on the southwest. An airfield ran parallel to the northwest shore and most of the support facilities were built along the road-lined southwest shore. Most of the island was lightly covered with brush and scattered palms, but the east-central position had a thicker covering of palms and underbrush and the north corner was covered by very dense brush. The surrounding coral reef was broad and flat with no natural obstacles on the lagoon side.
Eniwetok Island is two miles long from the northeast to the southwest and a quarter-mile wide near the southwest end. It was unique among the atoll’s islands in that the lagoon side was faced with a steep 8–15ft (2.4–4.6m) bluff immediately behind the narrow beach, presenting a difficult obstacle. A road ran most of the island’s length but only limited support facilities had been built. Along the southern portion of the lagoon shore the reef extended 200–500yds (183–457m), but presented no major obstacle, while along three-quarters of the rest of the island’s lagoon side there were broken fringing reefs and coral outcroppings.
Parry is a teardrop-shaped island two miles long and 600yds (549m) wide near its north end. A road followed the circumference of the shoreline. A small seaplane base was located on the upper central portion of the lagoon side as was a radio direction-finding station. The low, flat island is densely covered with palm and brush, although the upper portion of the west side is fairly clear. On the lagoon side the reef fringes the shoreline for most of the island’s length, but along the upper central portion it is free of reefs, although there are some coral outcroppings offshore as well as off the lower west shore.
Four other atolls were significant in the campaign: Jaluit, Maloelap, Wotje, and Mille would be by-passed. Cutoff from reinforcement, incapable of any offensive action owing to the destruction of all aircraft and seagoing vessels, these islands merely became targets being relentlessly bombed until the war’s end.
Jaluit Atoll is located near the south end of the western Ralik Group. Kwajalein Atoll is 245 miles (394km) to the northwest. Wotje and Maloelap Atolls are in the central portion of the eastern Radak Group while Mille Atoll is at the south end of the group. Majuro Atoll is situated between Maloelap (98 miles/157km north) and Mille (65 miles/105km southeast). Wotje is 164 miles(264km) east of Kwajalein, Maloelap is 70 miles (113km) southeast of Wotje, and Mille is 165 miles (266km) south-southeast of Wotje.
Jaluit is about 12 miles (19km) across its broader southern end from East to West Points, but only 4 miles (6.4km) wide at its north end, and almost 30 miles (48km) long from west-northwest to east-southeast. Of its 50 islands the largest is the long, narrow, L-shaped (with an extremely long vertical arm) Jaluit Island. Jabur Island was the administrative center of the Marshalls and the Japanese developed a major naval base on Jaluit Island, but with only a seaplane base and no airfield.
Maloelap is 30 miles (48km) long from northwest to southwest and 8–15 miles (12.9–24.1km) wide. The largest of its 64 islands are on the southeast end. An airfield was located on Taroa Island and the US considered it to be the most important Japanese airfield between Tarawa and Truk.
Wotje Atoll is 30 miles long from east to west and 8–12 miles (12.9–19.3km) across. Most of its 65 islands are found along is east rim, where the largest islands are located, the central south side, and a few scattered along the western north side. The largest island is Wotje Island on the extreme east-central end. An airfield and a seaplane base were located there.
Mille Atoll is 20 miles (32.2km) long from the west-northwest to the southeast and about 10 miles (16.1km) across. Its 30 islands are distributed around most of the atoll’s rim with the east side being open. A large airfield was built on the main Mille Island. This was the only airfield in the Marshalls that was within Japanese fighter range of the Gilberts to the southeast. It was from there that some of the strikes were flown against Tarawa and Makin during the Gilberts campaign.