The battle of Roi (1 February 1944) saw the US marines captured the main Japanese airbase in Kwajalein Atoll in a single day, after the Japanese defences were almost destroyed by the pre-invasion bombardment.
Roi and Namur were to be attacked by the Northern Attack Force (Task Force 53) under Rear Admiral Richard L. Conolly and the Northern Landing Force, made up of the 4th Marine Division (Major General Harry Schmidt). Admiral Conolly commanded the invasion from the command ship USS Appalachian.
Admiral Conolly's attack force consisted of three old battleships, 2 heavy cruisers, 2 light cruisers 10 destroyers, 2 high speed transports (APDs), 3 escort carriers, 12 LCIs and 4 mine sweepers.
Roi Island was almost clear of ground cover, as it contained the biggest Japanese airfield in the atoll, with three runways, four turning circles, two service aprons, two hangers, thirty revetments and a control tower. The island is 1,250 yards north-south and 1,200 yards east-west. The airfield on Roi was the HQ of all Japanese air power in the Gilberts and Marshalls.
Roi and Namur were connected by a beach on the lagoon side and a causeway half way between the atoll and the ocean. The ocean side was unsuitable for landings, but at high tide the reefs on the lagoon side were under water.
The plan was to capture a number of outlying islands on D-Day, then invade Roi and Namur from the lagoon side on D+1 (1 February 1944). Roi was to be attacked by the 23rd Regimental Combat Team, which was to land two regiments side by side on Red Beaches 2 and 3. A wave of LCI(G)s and armoured LVTs would lead the way, with the troops following in amphibious tractor.
On 29 January TG 58.2 (Essex, Intrepid and Cabot) attacked Roi-Namur, where the Japanese still had 92 aircraft. The carrier attack quickly eliminated the threat, and no Japanese aircraft were in the air after 0800. The same group attacked again on 30 January.
Roi and Namur between them were the most heavily defended part of Kwajalein Atoll. There was a battery of two 12.7cm dual purpose guns at the north-western corner of Roi. There was a 37mm position at the south-western tip of the island and another of the south-eastern tip. A number of 13.2mm single mount dual purpose guns were mounted along the ocean shore and six 20mm AA guns were scattered across the island. There were three concrete blockhouses on Roi, at the north-western, south-western and north-eastern corners. These guns supported four strong points, stretched out along the ocean shore. There were probably around 3,500 Japanese personnel on Roi and Namur, but it isn’t clear how many of them were effective combat troops. There were probably 345 fully effective troops, 2,150 partially effective air force personnel and around 1,000 or so ineffective personnel.
The naval bombardment began at 0651 on 31 January when the Biloxi and Maryland opened fire. The landings were also supported by the battleships Tennessee and Colorado, the heavy cruiser Louisville, the light cruiser Santa Fe, the escort carriers Sangamon, Suwanee and Chenango, seventeen destroyers, one destroyer escort and three mine sweepers. The gun fire stopped at 0715 to allow for an air strike, and resumed eight minutes later. A second air strike came in at 0825, followed by more naval gunfire.
All of this helped cover the capture of the five islands nearest to Roi and Namur - Jacob, Ivan, Albert, Allen and Abraham - all of which were used as artillery bases during the main invasions.
Roi was to be invaded by the 23rd Marine Regimental Combat Team, which was to land two battalions side by side on Red Beach 2 and Red Beach 3, on the southern, lagoon side, of the island. The first wave would be made up of LVT(A)s, followed by the troops in LVTs. The attack would be supported by LCI(G) gunships. The original plan was for the troops to transfer to LSTs on 31 January and then from the LST to the LVTs on 1 February, all outside the lagoons. This was changed after the chaos on D-Day, and the LSTs moved into the lagoon before disembarking the LVTs.
At 0645 the 3rd and 4th Battalions, 14th Marines, opened artillery fire from the nearby islands. At 0650 Santa Fe, Maryland, Indianapolis, Biloxi, Mustin and Russell opened fire on Roi. At the same time the 23rd Marines were prepared to move to the LVTs of the 4th Amphibian Tractor Battalion, which hadn't been involved on 31 January. However this didn’t mean that everything went smoothly. The crews of the LSTs were inexperienced, and most of their ships were new. There were a series of mechanical problems lowering the LVTs. The landings had to be postponed and the naval bombardment extended. Eventually the signal to land was given at 1112, some two hours late!
The troops were led in by LCI(G) gunboats, followed by LVT(A)s. The infantry came next, and were followed by tanks in LCMs. The LVT(A)s of the 1st Battalion, 23rd Marines, landed at 1133 and advanced to the anti-tank ditch near the coast to provide fire support. The first two waves of infantry were ashore by 1158. The first wave of the 2nd Battalion landed on the right at 1150.
The main effort was made on the right, where the 2nd Battalion had the task of advancing up the east coast of the island to clear out the main cluster of buildings around the airfield. They were allocated a company of LVT(A)s and most of the division's medium tank company. The first attempt to land the medium tanks went wrong when their LCMs ran aground having missed the channel through the reef. However the water was shallow enough for the tanks to be able to wade ashore. They were then able to cross the anti-tank ditch, and advance across the island.
The pre-invasion bombardment had been very effective on Roi. There was very limited opposition immediately after the landings, although one pillbox in the middle of the sand spit between Roi and Namur opened fire. The advance across the airfield began ahead of schedule, after the tank commander decided not to risk sitting in an exposed position on the airfield. This caused some concern amongst the senior officers, who were worried that their disorganised men were vulnerable to attack, but the Japanese had been too badly battered by the pre-invasion bombardment to be a real threat.
The orders for a formal attack were issued at 1530. The advance went quickly, with little organised resistance. Some Japanese troops were found in the trenches facing out to the ocean, but this was soon overcome. A few pillboxes had survived, but were quickly knocked out. The north-eastern corner of the island had been cleared by 1700.
Some mopping up took place on 2 February, but the island had been secured by the end of the first day. Namur took a little longer to capture, but the entire operation was effectively over within three days.
Between them these two attacks cost the Americans 190 dead and 547 wounded, while the Japanese lost 3,500 dead and 264 captured