APOD Operation Flintlock – Smashing Through the Outer Defences
The Battle of Kwajalein/Roi-Namur took place from 31 January-3 February 1944 and completed the ruin of the outer Japanese defence line in the Pacific. In a stunningly successful attack Admiral Fletcher’s carriers had destroyed Japanese airpower in the Gilberts and Marshalls. This left the main base in the Marshalls (Kwajalein) essentially defenceless as Yamamoto was unwilling to fight yet another ‘decisive battle’ (not one of which had proved at all decisive) for the outer defences. The only strongly held position was the enormous safe anchorage at Kwajalein Atoll. Employing the hard-learned lessons of earlier battles the United States launched a successful twin assault on the main islands of Kwajalein in the south and Roi-Namur in the north. The Japanese defenders put up stiff resistance, although outnumbered they were well-prepared with what they had. The determined defense of Roi-Namur left only 51 survivors of an original garrison of 3,500. For the US, the battle represented both the next step in its island-hopping march to Japan and a significant moral victory because it was the first time the Americans had penetrated the outer ring of Japanese defences. For the Japanese, the battle represented the complete failure of the beach-line defence system on islands lacking defensive depth or significant terrain, so later Japanese defences became prepared in depth.
Kwajalein Atoll lay in the heart of the Marshall Islands, in the Ralik Chain, 2,100nm southwest of Hawaii WikiMiniAtlas
. Kwajalein is the world's largest coral atoll and comprises 93 islands and islets, it has a land area of 1,560 acres (6.33 km²), and surrounds one of the largest lagoons in the world, measuring 324 mi² (839 km²) in size. This lagoon was the American target, in it they could safely anchor the powerful afloat logistics system they had built.
The two most significant land masses are Kwajalein Island in the south, and the linked islands of Roi-Namur in the north. By the start of World War II, the were already an integral part of the Japanese perimeter of defense. Its facilities were being utilised as outlying bases for submarines and surface warships, as well as for air staging for future advances being planned against the Ellice islands, Fiji and Samoa.
After the capture of Makin in the Gilbert Islands, the next step in the United States Navy's campaign in the central Pacific was the Marshall Island chain. The strategic importance of the Marshalls had been recognized as early as 1921 in Plan Orange. The Marshalls were a key step in the island-hopping march to the Japanese mainland.
After losing the Solomon Islands and Papua (as well as some of New Guinea) to the Allies in 1943, the Japanese command decided that the Gilbert and Marshall Islands were expendable outworks, although they did reinforce them to bleed the Americans and define their strategic and operational methods. They preferred fighting a major fleet action deeper within their defense system where they could better coordinate their new combined land-carrier airstrike system. So the Marshalls were reinforced at the end of 1943 to make their capture more costly for the Americans. By January 1944, the regional commander in Truk, Admiral Masashi Kobayashi, had 28,000 troops to defend the Marshalls, although Admiral Fletcher had destroyed the available aircraft.
Japanese Planning and Preparations
The 6th Base Force, under the command of Rear Admiral Monzo Akiyama, and headquartered on Kwajalein since August 1941, was the principal defense force of the islands. Akiyama, however, had his men spread out over a very wide area, with IJN air bases located on Roi-Namur, Mille, Maloelap, Eniwetok, and Wotje. Garrison troops on the island included the 1st Company, 3rd Mobile Battalion, 1st Amphibious Brigade, plus units of the 2nd Mobile Battalion. The defense system on the islands was mostly in line, with little or no depth although there was really little choice in this matter. The Japanese had twin 5” guns on each end of the island in heavy fortification, plus 80mm guns on the ocean and lagoon sides, as well as 4.7” and 8” ‘short guns’ in concrete pits to take landing areas under indirect fire. These proved to be highly effective. The 22nd Air Flotilla, shattered during the Gilbert campaign, had been withdrawn to reinforce: by pushing the offensive so strongly, the USN got inside the Japanese cycle and this formation played only a small role with effective night-time torpedo bomber attacks.
US Planning and Preparation
The Marshall campaign planned by the US, involved attacks on seven islands, bypassing many more. Operation Flintlock had nine phases, the main phase being the capture of Kwajalein and Majuro Atolls, a second phase, Operation Catchpole, being the capture of Eniwetok, and remaining phases being the capture of remaining islands. Bombardment by the Seventh Air Force, and a carrier air attack on 4 Dec. 1943, followed by additional attacks in Jan. 1944, destroyed the handful of Japanese liaison and general purpose aircraft present. The 4th Marine Division—under Major General Harry Schmidt—was assigned to Roi-Namur, and the Army's 7th Infantry Division—under Major General Charles H. Corlett—would make the assault on Kwajalein.
Staging through Baker Island airfield, B-24 Liberators bombed strategic targets. In the beginning, the most important was Mili Atoll, the Japanese base closest to the Gilberts and Maloelap, the most powerful enemy bases threatening the upcoming operations. Mili was the subject of several attacks throughout November, causing considerable damage to installations and knocking out the runways. Weekly raids to keep it that way averaged 106 B-24s using 111 tons of bombs. The largest of those raids came on 4 December when 34 B-24s hammered the atoll in conjunction with carrier-based bombing raids of other parts of the Marshalls. On 18 December, renewed strikes were initiated against enemy targets on Mili with USAAF land-based Douglas A-24 Banshee dive bombers and Bell P-39 Airacobra fighters making their debut in the Marshall air offensive.
It was necessary to take another atoll in the eastern Marshalls, Majuro 190 nm southeast of Kwajalein. Majuro was undefended and only the V Amphibious Corps Marine Reconnaissance Company and the 2nd Battalion, 106th Infantry, 7th Infantry Division were employed in its capture.
The U.S. forces for the landings were Rear Admiral Richmond K. Turner's 5th Fleet Amphibious Force, and Major General Holland M. Smith's V Amphibious Corps, which comprised the 4th Marine Division commanded by Maj. Gen. Harry Schmidt, the Army's 7th Infantry Division commanded by Maj. Gen. Charles H. Corlett, as well as the 22nd Marines, and the Army's 106th and 111th Infantry regiments. The 4th and 7th Divisions were assigned to the initial landings at Kwajalein, while the 2nd Battalion of the 106th was assigned to the simultaneous capture of Majuro Atoll. The rest of the 106th and the 22nd Marines were in reserve for Kwajalein, while awaiting the following assault on Eniwetok, scheduled for three months later.
The 7th Infantry Division began by capturing the small islands labeled Carlos, Carter, Cecil, and Carlson on 31 January, which were used as artillery bases for the next day's assault. Kwajalein Island is 2.5 miles long, but it is only 880 yards wide. There was therefore no possibility of defence in depth, and the Japanese planned to counter-attack the landing beaches. They had not realised until the battle of Makin that American amphibious vehicles could cross coral reefs and land on the lagoon side of an atoll; accordingly the strongest defences on Kwajalein faced the ocean because the defences could not be ‘turned around’ in the available time (although what could be done was done). The bombardment by the Southern Attack Force, heavy B-24 strikes and artillery on Carlson island was devastating. The Official U.S. Army history of the battle quotes a soldier as saying "the entire island looked as if it had been picked up 20,000 feet and then dropped." Landing beaches Red 1 and 2 were assaulted at 0930 on 1 February and here the US forces suffered heavy losses from the remaining one 8” and four 4.7” ‘short guns’ firing shrapnel at the beaches. These guns were later assessed as responsible for nearly a thousand casualties, of which 155 were killed. The Americans reaching half-way across the runway by sunset. Although the Japanese counterattacked every night, the island was declared secure by the end of the fourth day.
On the north side of the atoll, the 4th Marine Division followed a similar plan, first capturing islets Ivan, Jacob, Albert, Allen, and Abraham on 31 January, and then landing on Roi-Namur on 1 February. The airfield on the western half (Roi) was captured quickly, and the eastern half (Namur) fell the next day.
The situation was slightly less rosy at sea. Although caught totally off balance and essentially unable to respond in strength, they used what they had available to hit the US supply lines. There was only one major attack on the US Fleet although Japanese knowledge of USN movements, locations and dispositions was excellent due to their un-interceptable daylight reconnaissance aircraft and fast radar-fitted night time reconnaissance capability.
1/2 Feb 43
A force of 18 new Mitsubishi Ki-67 (known in IJNAF service as the P1M1 Yasukuni) torpedo bombers, supported by 12 G4M3 radar-fitted flare droppers stalked the CVE support group and conducted a waterfall attack on it between 2330 and 0100. This was the combat debut of the P1M1 in the Pacific and these crews, while not green, were less experienced. This, and their small numbers, was the reason they were sent against a secondary target. The radar-fitted flare droppers took some time to localise the target, due to their radical maneuvers – six attacks were reported before the attack went in. The P1M1 concentrated on two CVE (USS Breton and USS Chatham) and hit both. USS Breton was hit twice and suffered a heavy internal explosion aft, about 15 minutes after being hit. She sank rapidly. USS Chatham was also hit twice, losing all power and catching fire. Without power for the pumps the fire spread and became uncontrollable. The ship was abandoned but remained afloat until sunk next day by a Japanese I-boat.
CVE USS Breton torpedoed and sunk
CVE USS Chatham torpedoed and sunk
At the time, Fletcher considered this ominous, and he was right to do so. He had no idea that the Combined Fleet, which had been assembling at Palau to head south-west and crush the spoiling offensive, had been redirected by Yamamoto. What he did know was that the Australians were keeping a tenuous eye on Truk with ‘cottonised’ B.20 Brisbane ‘Night Angel’ fast flying boats and that they reported that it had been empty for weeks, with no sign of significant IJN activity anywhere except out of Kuching. Fletcher had a suspicious mind, and was casting his own reconnaissance web wide, but aside from submarines and light aircraft activity it too was coming up empty. As he reported to Hawaii, he appreciated that the Imperial offensive far to the west had pulled off the guardians – but it had to be the calm before the storm. He began the task of changing his air groups, moving his torpedo bombers (the Avenger was the physically largest aircraft in his hangars) back to the CVE and replacing them with more fighters, which made his remaining Helldivers his major striking arm.