This was the US seizure of the southern portion of the Marshall islands group within the ‘Bankrate’ plan (30 January/4 February 1944).
The Battle of Kwajalein was a significant part of the Pacific campaign. Benefiting from the lessons which had been learned at so great a cost in the 'Galvanic' operation against Tarawa atoll, and more specifically in the 'Longsuit' seizure of Betio in this atoll during November 1943, the US forces launched 'Flintlock' as a twin assault on the main islands of Kwajalein in the island group’s southern area and the smaller islands of Roi and Namur in its northern area.
For the USA the battle was both the next step in its progressive island-hopping approach to the Japanese home islands and a significant moral victory because it was the first time the US forces had penetrated the outer perimeter of the Japanese empire in the Pacific. For the Japanese, the battle represented the failure of their established concept of cordon defence on the beach, and after this Japanese defences became prepared in depth, and the battles of the Palau islands Group ('Stalemate II') and the Mariana islands group ('Forager') proved far more costly to the USA.
The atoll of Kwajalein lies in the heart of the Marshall islands group. It is part of the Ralik islands chain, some 2,400 miles (3860 km) to the south-west of Honolulu in the US Hawaiian islands group, is one of the world’s largest coral atolls in terms of the 839-sq mile (2174-km²) area of its lagoon, and comprises 97 islands and islets with a total area of only 6.33 sq miles (16.4 km²). The atoll’s two most significant land masses are Kwajalein island in the south, and the linked islands of Roi and Namur in the north.
Kwajalein atoll is 66 miles (106 km) long, and its lagoon possesses an essentially unlimited ship capacity together with unfettered access by means of 25 passes up to 120 ft (36.5 m) deep. In naval terms, the atoll’s large number of passes was its primary liability as this made the anchorage difficult to protect from submarines.
Kwajalein was the principal Japanese base in the Marshall islands group, which were seized from the Germans by the Japanese in 1914. After World War I’s end, Japan received a League of Nations mandate over the islands in 1920, but refused to turn the islands back over to the league after withdrawing from this latter in 1933. This led to considerable mystery over the extent to which Japan had fortified the islands during the 1930s, for foreigners were excluded from most of the Japanese mandate territories.
The islets of the atoll had ample room for military airfields, but the two which were in fact built were one on Kwajalein islet at the southern end of the lagoon and the other at the atolls’s north-eastern angle on Roi-Namur, which are two islets that were originally joined by a causeway and subsequently silted together into a single islet. The Roi airfield, which covered almost the entire 1,250- by 1,170-yard (1145- by 1070-m) area of the islet, eventually boasted one 4,365-ft (1330-m) and two 3,610-ft (1100-m)) runways, together with facilities for 72 torpedo bombers and 100 fighters. Measuring 800 by 890 yards (730 by 815 m), Namur hosted the support facilities and had a 445-ft (135-m) pier across the reef to the lagoon. The reef on the ocean side of both islets is 125 to 450 yards (115 to 410 m) wide and drops abruptly which, in combination with the prevailing trade winds, makes for heavy surf. On the lagoon side, the reef slopes more gradually and had much lighter surf, and it was on this side that the US forces opted to make their 'Flintlock' landings.
Kwajalein airfield had a 3,925-ft (1200-m) runway. The island itself is crescent-shaped, some 2.5 miles (4 km) long and 800 yards (730 m) wide, and was covered with palms and salt brush, particularly on its northern side. There was a sea wall doubling as an anti-tank wall along its shore and a road circling the entire island. There were two small 100-yard (90-m) piers on the centre of the northern shore of the island’s southern half, and the much larger 505-yard (460-m) Nob Pier on the western shore of the northern part of the island. The reef is 100 to 130 yards (90 to 120 m) wide on the ocean side and is completely exposed at low tide, with heavy surf at high tide. The reef on the lagoon side is 500 to 800 yards (460 to 730 m) wide and studded with coral heads, but has light surf, and as with Roi-Namur the US forces chose to make their landings on the lagoon side of the island.
At the north-western angle of the atoll, Ebadon islet was also large enough for an airfield, though none was constructed during the war. There was a seaplane base at Ebeye just to the north of Kwajalein on the eastern face of the atoll.
Kwajalein was the headquarters of 6th Fleet, the Japanese submarine force, whose submarines took up positions in the Hawaiian islands area before the 'Ai' attack of December 1941 on Pearl Harbor, when its commander was Vice Admiral Mitzumi Shimizu, and was also the mustering point for the Wake Island Invasion Force in December 1941.
By the start of World War II, the Marshall islands group had been fully integrated into the Japanese empires’s outer defensive perimeter. The Japanese built facilities for the island group’s use as an outlying base for submarines, surface warships and aircraft with a view to later advances being planned against the Ellice, Fiji and Samoa island groups.
After the 'Galvanic' capture of Makin and Tarawa islands in the Gilbert islands group, to the south-east of the Marshall islands group, the next step in the campaign spearheaded by Admiral Chester W. Nimitz’s Pacific Ocean Areas command in the central Pacific was the Marshall islands group. Since being allocated to Japan after World War I, these islands had become something of a mystery as the Japanese had closed them to the outside world. It was presumed the Japanese had built illegal fortifications throughout the islands, but the extent and nature of any such fortifications was unknown. The Japanese regarded the islands as part of the outer ring of the Japanese empire in the period before its entry into World War II, and the US assault would be the first against what the Japanese regarded as Japanese soil.
The strategic importance of the Marshall islands group had been identified as early as 1921 in 'War Plan Orange', the US colour-coded inter-war plan for a possible conflict with Japan, and from this time onward was regarded as a key step in the USA’s proposed island-hopping approach to the Japanese home islands.
After the loss of the Solomon islands group and New Guinea to the Allies in 1943, the Japanese command decided that the Gilbert and Marshall island groups would now be regarded as expendable as the Japanese came to prefer the concept of fighting the decisive battle at a location closer to the home islands. At the end of 1943, however, the Japanese reinforced the Marshall islands group to make their capture notably costly for the Americans. By January 1944, the regional commander on Truk atoll, Vice Admiral Masami Kobayashi, had 28,000 troops with which to defend the Marshall islands group, but only very few aircraft.
US air attacks during 1943 had persuaded the Japanese to withdraw their ships from the major naval base at Jaluit atoll to Truk atoll in the eastern part of the Caroline islands group. Kobayashi’s 4th Fleet, headquartered at Truk, was responsible for the defence of the Marshall islands group, where its main operating unit was the 6th Base Force. This had arrived in March 1941 and was first based on Wotje before being relocated to Kwajalein during August. Later in the same year guard forces arrived to garrison the islands. Japanese naval air bases in the Marshall islands included landplane fields on Roi at the northern end of Kwajalein, Mille, Maloelap, Wotje, and Eniwetok, as well as an uncompleted field on Kwajalein, and seaplane bases at Jaluit, Wotje, Majuro, Taongi and Utirik. Regardless of all these airfields, by the time of the US invasion there were only a few aircraft remaining on Eniwetok, the others having been destroyed by the steady weight of carrierborne and bomber air attacks.
On 1 February 1942 a US carrier task force ventured into the Marshall islands and launched air attacks on Jaluit, Kwajalein, Milli, Maloelap and Wotje, and also on Makin in the Gilbert islands group. While these attacks unsettled the Japanese, they inflicted little real damage. In September 1943 the Imperial General Headquarters designated a new National Defence Zone anchored in the Mariana and Caroline island groups, and running through the eastern portion of Netherlands New Guinea. The Solomon and Bismarck island groups, as well as the eastern part of New Guinea, had already been lost or were about to be lost. The Marshall islands group, while outside this zone, was not abandoned, and it was decided that a delaying action could be fought there to buy further times for the defences of the new zone to be properly established. The Japanese navy was tasked with sending units from Japan, the northern part of China and the Philippine islands to support the delaying action. Units reorganised as South Seas Detachments and the new 1st Amphibious Brigade were sent to Kwajalein, Jaluit, Maloelap, Wotje, Mille and Eniwetok late in 1943 and during January 1944.
While the defences on the Marshall islands were improved, they were never substantial or strongly manned. After nearly 10 years of construction, the defences on the Marshall islands were considerably inferior to those of Tarawa, which had been turned into a fortress in less than 18 months.
The inadequate strength of the fixed defences was further degraded by the fact that fewer than half of the troops stationed in the Marshall islands group were combat trained, the greater number being support and labor troops with, at best, limited combat training. It was not until after the Japanese position in the Solomon islands group and New Guinea began to deteriorate that Imperial General Headquarters made further plans for the strengthening of the defences of the Marshall islands group. As noted above, by September 1943 the Japanese high command had in effect written off the Gilbert and Marshall islands groups, deciding that these should be used for the fighting of delaying actions while a new defence perimeter was created from the Banda Sea through Caroline and the Mariana island groups. Combat units were ordered to the Marshall islands group from the Philippine islands group, Manchukuo and the home islands, with additional air strength to be flown in from both the home islands and Truk.
The 6th Base Force, under the command of Rear Admiral Monzo Akiyama, was headquartered on Kwajalein as the principal defence force of the islands. Akiyama spread his men over a very wide area, concentrating mostly on the defence of the Jaluit, Mille, Maloelap and Wotje islands which were never considered vulnerable to US attack. The reinforcement troops included the 2/1st Amphibious Brigade under the naval Captain Aso, nine Type 94/97 tankettes and two companies of Type 2 amphibious tanks of the Kwajalein Tank Detachment. When these armoured vehicles arrived, they were quickly dispersed by Akiyama, mainly to the outlying atolls.
In overall terms, therefore, the defence of Kwajalein was undermanned, unprepared and generally poorly equipped to face the assaults being planned for its seizure. The Japanese manpower on the islands was about 8,000 men of whom, as noted above, fewer than half were combat troops. On Kwajalein proper, the men were mostly construction troops, many of them impressed Koreans. On Roi-Namur, the troops were mostly Japanese naval air force personnel with little in the way of weapons or training for ground combat.
The Americans estimated, moreover, that even before the landings were made the Japanese had lost between 50% and 75% of their men killed or wounded by the US Navy’s and USAAF’s bombardment. Even though this estimate may have been too great, it is nonetheless clear that Japanese had suffered very significant losses just from the naval and air firepower launched at them before the landings began.
The Japanese defence system on the islands was mostly linear, with little or no depth. Although there were a number of fortified areas, none of these was as large or as well armed as those of Tarawa. In addition, there were several defences that had been created in expectation of an assault from the ocean rather than the lagoon. No coastal defence artillery had been emplaced on key islets guarding passages to the lagoon, and there was little or no use of mines.
Despite these and other deficiencies, the Japanese maintained their effort to strengthen ground defences. Akiyama’s greatest defence nonetheless remained in his offensive aircraft operating from the well-manned bases on Roi-Namur, Maloelap, Wotje, Mille and Eniwetok, as well as the Mitsubishi A6M Reisen 'Zero' fighters of the Chitose Kokutai and 653rd Kokutai and Mitsubishi G3M 'Nell' and Mitsubishi G4M 'Betty' long-range bombers operating from the nearly completed base on Kwajalein. In addition, the Japanese had some Nakajima A6M2-N fighter and Mitsubishi F1M reconnaissance floatplanes detached to the seaplane bases on Jaluit, Wotje, Majuro, Taongi, Utirik and the south Kwajalein atoll island of Burton.
During November 1943 bombers attacks by USAAF land-based and US Navy carrier-based aircraft, in conjunction with the 'Galvanic' assault on the Gilbert islands group, had destroyed 71 of Akiyama’s fighters and bombers. Reinforcements flown in from the home islands and Truk replenished many of these losses, Akiyama could expect little additional help in the future. The Japanese war industry was by now falling far short of the production rate that was required, affecting all branches of the armed force including the carrierborne air arm, which had already retreated from the central Pacific. In fact, the 32 aircraft flown from Truk were the last of the carrierborne aircraft which had been left there in the wake of that retreat. Akiyama was therefore expected not to defeat the US assault, but rather to delay the US forces advance while also inflicting the greatest possible losses on them.
Within the concept of the US Navy-led drive through the Central Pacific toward the Japanese home islands, this operation was the logical successor to the ‘Galvanic’ capture of the Gilbert islands to the south during November 1943. As well as providing the forward bases necessary for this next step toward Japan, the operation also threatened the main base of Admiral Mineichi Koga’s Combined Fleet at Truk in the Caroline islands group away to the west.
Even though the capture of the Marshall islands group had been embodied in the USA’s pre-war ‘War Plan Orange’ scheme of colour-coded contingency plans, it had not been decided which of the atolls were to be captured, and in what order they were to be assaulted. Expecting the US forces to make their initial move against the outermost islands of the group, the Japanese had stationed most of their defenders on the atolls of Wotje, Mille, Maloelap and Jaluit to the east and south. Indeed, the original US plan had called for a cautious series of sequential attacks starting in the eastern part of the Marshall islands group.
The Japanese troop dispositions were revealed to the Americans by ‘Ultra’ decrypts of Japanese signals, and over the objections of many of his senior operational commanders, Nimitz followed the suggestion of Rear Admiral Forrest P. Sherman, deputy chief-of-staff of the Pacific Fleet and Nimitz’s senior planning officer, that Kwajalein should be the first objective regardless of the fact that it lies in the centre of the group and that the assaulting forces could therefore be attacked by Japanese land-based aircraft from others of the group’s atolls, most notably Jaluit, Maloelap, Mille and Wotje, which could also accommodate larger numbers of aircraft staging from the Mariana and Caroline island groups.
Access to ‘Ultra’ intelligence made first Sherman and then Nimitz rightly confident that Kwajalein was the perfect objective for the initial assault, and they were also sure the US forces involved could be adequately covered from air attack by Rear Admiral Marc A. Mitscher’s Fast Carrier Task Force (Task Force 58) of Vice Admiral Raymond A. Spruance’s 5th Fleet, to which overall control of ‘Flintlock’ was entrusted.
Preliminary air raids against Kwajalein had begun as early as 4 December 1943, when Rear Admiral Charles A. Pownall took a significant part of the Fast Carrier Task Force on a raid against Kwajalein 1. In several attacks by 386 carrierborne aircraft, six transports totalling 25,316 tons were sunk, and three ships totalling 17,249 tons as well as the light cruisers Isuzu and Nagara were damaged. However, the incoming attacks had been detected by the Japanese, who were able to put about 50 fighters into the air, and the results were less than had been anticipated. Pownall withdrew at once, citing the exhaustion of his pilots and the lack of night-fighter support. During the US withdrawal, Japanese torpedo-bombers of the 752nd Kokutai and 753rd Kokutai obtained one torpedo hit on Lexington's stern, and this rendered the carrier unsteerable for 20 minutes. The cruiser Mobile and destroyer Taylor were slightly damaged by US defensive fire. Some 55 Japanese aircraft were shot down or destroyed on the ground. Only five US aircraft were lost.
At the same time the fleet carrier Yorktown made a diversionary raid on Wotje.
On 8 December Rear Admiral Willis A. Lee’s TG50.8 2 attacked Nauru, bombarding the island with 810 rounds from their 16- and 5-in (406- and 127-mm) guns. In response, a Japanese coastal battery damaged Boyd. Air escort was provided by the warplanes of the fleet carrier Bunker Hill and light fleet carrier Monterey.
Attacks by long-range bombers in January 1944 failed to effect the complete suppression of Japanese air power in the Marshall islands group, but beginning on 29 January a series of powerful attacks by carrierborne aircraft annihilated the remaining Japanese aircraft.
Under Mitscher’s command, TF58 attacked the Japanese bases in the Marshall islands group. Rear Admiral John W. Reeves’s TG.58.1 3 attacked Maloelap on 29 January, and Kwajalein on 30 and 31 January and then up to 3 February. Montgomery’s TG58.2 4 attacked Roi from 29 to 31 January and then from 1 to 3 February. The attacks of 29 January destroyed 92 of the 110 Japanese aircraft in the Marshall islands group.
Rear Admiral Frederick C. Sherman’s TG58.3 5 attacked Eniwetok from 30 January to 2 February. Rear Admiral Samuel P. Ginder’s TG58.4 6 attacked Wotje on 29 January, Maloelap on 30 and 31 January and, after refuelling on 1 February, Eniwetok from 3 to 6 February.
These attacks were very carefully co-ordinated, with top cover by Grumman F6F Hellcat fighters to intercept any Japanese fighters while additional Hellcat aircraft operated as fighter-bombers to strafe aircraft revetments, Douglas SBD Dauntless dive-bombers attacked anti-aircraft positions, and Grumman TBF Avenger bombers dropped clusters of fragmentation bombers on revetments and 2,000-lb (907-kg) bombs to crater runways. The last Japanese aeroplane seen over Kwajalein was shot down on 29 January. The cost to the Americans was 49 aircraft (22 aircraft to the Japanese defences and the other 27 in accidents) and 48 aircrew out of 6,232 sorties, of which 4,021 were attack sorties.
In addition there was the TG50.15 'neutralisation group' comprising the heavy cruisers Chester, Pensacola and Salt Lake City, and destroyers Erben, Walker, Hale and Abbott). On 30 January the battleships Washington, North Carolina, Indiana and Massachusetts, with the destroyers Ingersoll, Knapp, Burns, Caperton and Cogswell, bombarded installations on Kwajalein, North Carolina and Burns sinking three ships.
Between 26 and 31 January, US submarines deployed around Truk to prevent a relief sortie by Japanese surface vessels comprised Permit, Skipjack which sank one 6,666-ton ship and the destroyer Suzukaze, and Guardfish which sank one 10,024-ton ton and the destroyer Umikaze. Seal was deployed off Ponape, Sunfish off Kusaie, and Searaven off Eniwetok.
To cover the operation against Japanese air attacks from Wake island, Consolidated PB2Y Coronado flying boats bombed Japanese airfields on the island on 30 January and then again on 4, 8 and 9 February.
Land-based aircraft also had a part to play. Staging through Baker island, Consolidated B-24 Liberator heavy bombers of the 7th AAF attacked numerous targets. At first the most important of these was Mili atoll, the Japanese base closest to the Gilbert islands group, and Maloelap, which were the most powerful Japanese bases threatening the forthcoming operations. Mille was the subject of several attacks throughout November, causing considerable damage to installations and high losses of aircraft for the Japanese. But Mille remained the only base within fighter reach of the Gilbert islands group, and its defenders managed to keep the island’s facilities operational and reinforced with aircraft. Following the capture of Tarawa on 20/28 November 1943 and until 19 December, 106 B-24 bombers dropped 109 tons of bombs on Mille’s air base. The largest of the raids was that of December when 34 B-24 bombers pulverised the atoll in conjunction with carrier-based bombing raids of other parts of the Marshall islands group. On 18 December attacks were initiated against targets on Mille with Douglas A-24 Banshee land-based dive-bombers and Bell P-39 Airacobra fighters which were making their debut in the Marshall islands' air offensive. Japanese losses for the day amounted to 10 fighters (four on the ground) and four damaged. Other aircraft types participating in the offensive included the North American B-25 Mitchell medium bomber and Curtiss P-40 Warhawk fighter-bomber.
The 5th Fleet’s major assault element was Rear Admiral Richmond K. Turner’s 5th Amphibious Force (including Major General Holland M. Smith’s V Amphibious Corps) with TF58 sweeping ahead of it to eliminate Japanese air strength on the Marshall islands.
At the suggestion of Spruance’s chief-of-staff, Rear Admiral Carl Moore, Majuro atoll had been added to the list of objectives for 'Flintlock', and indeed was selected for the operation’s first assault as its deep lagoon would provide the ships of the 5th Fleet with a safe fleet anchorage in which to refuel, resupply and undertake repairs. Spruance and Moore had become concerned that the planned areas for refuelling at sea would be subject to attack by land-based aircraft, and wished to use the atoll as a secure base for refuelling. Once completed, airfields on Majuro would also protect the supply line to Kwajalein against attacks from the isolated Japanese garrisons to the north and south.
The invasion force was Rear Admiral Harry W. Hill’s TG51.2, with one attack transport, two troop-carrying destroyer conversions, one tank landing ship and two minesweepers, escorted by the escort carriers Nassau and Natoma Bay, heavy cruiser Portland, and destroyers Bullard, Black, Kidd and Chauncey.
Majuro is an atoll in the eastern part of the Marshall islands group some 220 miles (355 km) to the south-east of Kwajalein and could serve as an advanced air and naval base, and its seizure would sever the Japanese supply lines to Kwajalein.
Following the bombardment by aircraft and, on 30 January, by battleships of TG58.1, the landings were made on 31 January with fire support from the warships of TG52.8 and TG53.5. During the bombardment operations on 1 February the cruiser Louisville was hit accidentally by a shell from the cruiser Indianapolis, the destroyers Anderson, Haggard and Colahan were damaged after running aground, and the battleships Washington and Indiana were damaged in a collision.
In the event Majuro proved to be very lightly defended, and only the V Amphibious Corps' Marine Reconnaissance Company and the 2/106th Infantry of Major General Charles H. Corlett’s 7th Infantry Division were employed in its capture on 31 January without US casualties.
The new base became operational just two days later, in part because the Japanese had abandoned a considerable quantity of equipment which was put to good use by the garrison force. Airstrips were constructed on Dalap and Darrit islets on the eastern side of the atoll. The Dalap strip was 5,800 ft (1770 m) long and was operational by 12 February, by which time there were 5,000 men, including the 1st Marine Defense Battalion, on the atoll.
Majuro then became a major forward base for the Fast Carrier Task Force. A 4,000-ft (1220-m) fighter airstrip was constructed on Uliga, between Dalap and Darrit, and a paved road 35 miles (56 km) long was constructed around the atoll, to which some 4,000 islanders were delivered after they had been rescued by submarine from Japanese-controlled atolls.
As noted above, while the amphibious force and its carrier support element were prepared for ‘Flintlock’, the atolls of the Marshall islands were pounded by army and navy aircraft operating from land bases on Makin and Tarawa atolls in the Gilbert islands group.
For ‘Flintlock’, Spruance’s 5th Fleet comprised two major elements in the form of Richmond K. Turner’s landing fleet and Holland M. Smith’s landing troops. Hill’s Southern Landing Force (TF52) had two troop-carrying destroyer conversions, 12 attack transports, three attack cargo ships, three landing ship docks, 16 tank landing ships and 12 infantry landing ships to land Corlett’s 7th Division on Kwajalein. Escort was provided by the destroyers John Rodgers, Hazelwood, Haggard, Franks, Schroeder and Hailey; fire support by Rear Admiral Robert C. Giffen’s TG58.2 with the battleships Idaho, Pennsylvania, New Mexico and Mississippi, heavy cruisers Minneapolis, New Orleans and San Francisco, and destroyers McKee, Stevens, Bailey, Frazier, Hall, Meade, Colahan, Murray, Harrison, Ringgold and Sigsbee; and air support by Rear Admiral Ralph E. Davison’s TG52.9 with the escort carriers Manila Bay, Coral Sea and Corregidor, and destroyers Bancroft, Coghlan, Caldwell and Halligan.
Rear Admiral Richard L. Conolly’s Northern Attack Force (TF53) had 12 attack transports, three attack cargo ships, two dock landing ships and 15 tank landing ships to land Major General Harry Schmidt’s 4th Marine Division on Roi. Escort was provided by the destroyers Remey, MacDonough, La Valette, Fletcher, Hughes, Ellet and Aylwin; fire support by Rear Admiral Jesse B. Oldendorf’s TG53.5 with the battleships Tennessee, Colorado and Maryland, heavy cruisers Louisville and Indianapolis, light cruisers Mobile, Santa Fe and Biloxi, and destroyers Morris, Anderson, Mustin, Russell, Porterfield, Haraden, Hopewell, Johnston and Phelps; and air support by Rear Admiral Van H. Ragsdale’s TG53.6 with the escort carriers Sangamon, Suwanee and Chenango, and destroyers Farragut, Monaghan and Dale.
The ‘Flintlock’ operation descended on Kwajalein during 1 February in the form of two distinct operations at opposite ends of the atoll, which is 44 miles (71 km) from north to south.
Under the tactical control of Conolly’s Northern Attack Force, Schmidt’s 4th Marine Division first took first capturing five nearby islets to serve as artillery bases to support the next day’s main assault. In this the 4th Marine Division landed its 23rd and 24th Marines on Roi and Namur, at the northern end of the lagoon, against 345 naval infantry of the 61st Naval Guard Force, 1,655 naval airmen, and 600 labourers under Rear Admiral Michiyuki Yamada, commander of the 24th Air Flotilla. The attack was confused, but the airfield on Roi (the eastern half), was captured quickly, and Namur (the western half), fell on the following day. The worst US setback came when a marine demolition team threw a high explosive satchel charge into what it believed to be a Japanese bunker, but was in fact a torpedo warhead magazine. The resulting explosion killed 20 marines and wounded many more. Only 51 of the original 3,500 Japanese defenders of Roi-Namur survived to be captured.
Under the tactical control of Turner’s Southern Attack Force, Corlett’s 7th Division began by capturing four nearby islets on 31 January for use as artillery bases for the next day’s assault. In this latter the division landed its 32nd and 184th Infantry on Kwajalein, at the southern end of the lagoon, against 1,750 infantry (900 soldiers of the 2/1st Amphibious Brigade and 850 naval infantry of the 61st Naval Guard Force reinforced by one company of the Yokosuka 7th Special Naval Landing Force) and perhaps 5,000 labourers, all under the command of Akiyama.
Given that they had no opportunity to create a defence in depth, the Japanese had planned to counter-attack the landing beaches. They had not realised until the battle of Tarawa that US amphibious vehicles could cross coral reefs and so land on the lagoon side of an atoll, and this was the reason why the strongest defences on Kwajalein faced the ocean. The bombardment by battleships, B-24 bombers from Apamama, and artillery on one of the nearby islets was devastating. By the time the 7th Division landed on Kwajalein on 1 February, there was little resistance and by the evening the Americans estimated that only 1,500 of the original 5,000 defenders were still alive.
By the fall of night on the first day, the 7th Division had landed six reinforced battalions and had reached the western end of the airfield. Then with the support of tanks, naval gunfire and support aircraft, the division methodically cleared the island in four days.
The US forces had learnt so much from their ‘Galvanic’ initial island operation of the central Pacific campaign that their tactics were much better and their losses commensurately lower than those of the assault on Tarawa.
By 7 February the Americans had landed 20,104 men in the north and 21,342 men in the south, and their losses were 372 killed and 1,582 wounded out of 42,000 men involved, while the Japanese lost 7,870 men.
The relatively easy capture of Kwajalein clearly proved the improving quality of US amphibious capabilities and showed that the changes to training and tactics after the bloody battle of Tarawa had been effective. It allowed Nimitz to speed operations in the Marshall islands group, and therefore to make the landings on Eniwetok atoll on 17 February 1944.
This was made feasible by the fact that the battle for Kwajalein had not required the deployment of the 5th Amphibious Force’s reserve (single army and marine regiments), and it was this which was then used for ‘Catchpole’, which took Eniwetok atoll in the north of the group and so completed the US seizure of the Marshall islands group. Some 12 mostly unoccupied atolls of the Marshall islands group and three of the area’s other islands were secured in March 1944 in ‘Flintlock Junior’.
The Japanese learned from the battle for Kwajalein that beach-line defences were desperately vulnerable to the bombardment of ships and aircraft. In 'Forager' and 'Stalemate II' campaigns for the Mariana and Palau island groups, the defence in depth on Guam and Peleliu proved much harder and bloodier to overcome than the thin beach defence line on Kwajalein.