Operation Catchpole (17-22 February 1944) saw the Americans conquer Eniwetok Atoll in the north-western corner of the Marshall Islands, giving them a good base for the advance into the Mariana Islands.
Eniwetok Atoll is almost circular. The main islands are all along the eastern side of the atoll. At the northern end of this line is Engebi Island. A series of smaller islands runs south-east and then south to Ladyslipper (Japtan) Island, at the northern end of the deep entrance into the atoll. Parry Island is at the southern end of the entrance. The eastern line ends with Eniwetok Island, the largest island in the Atoll. To the west of Eniwetok was a large gap - the wide passage. The atoll is 330 nautical miles to the north-west of Kwajalein, in the north-western Marshalls.
The original plan had been to occupy Eniwetok no earlier than 1 May 1944, probably as part of an attack on Truk or other bases in the Carolines. The 27th Infantry was allocated to this invasion, but would never be needed. Even before the start of the fighting at Kwajalein some work had been done on an earlier attack. Once Operation Flintlock was underway it was clear that the reserves - the 22nd Marines and most of the 106th Infantry - wouldn't be needed. On 2 February Admiral Nimitz asked Admiral Spruance for his thoughts on the idea of an early invasion. Spruance agreed with the idea, and the invasion was brought forward. On 3 February Admiral Hill, who had commanded the almost unopposed invasion of Majuro (31 January 1944) was given command of the operation.
The plan for Operation Catchpole was put together very quickly. It would be supported by a full scale carrier attack on the major Japanese base at Truk, carried out by Admiral Mitscher's fast carrier force (Task Force 58), to take place on 15 February.
Admiral Hill's force was known as the Eniwetok Expeditionary Group. His command ship was the modified attack transport Cambria, which had been given extra communications equipment to turn it into an amphibious headquarters ship.
The transport group consisted of five attack transports, one transport, two attack cargo ships, one cargo ship, one dock landing ship, two high speed transports, nine LSTs and six LCIs, supported by ten destroyers.
The naval fire support group (Rear Admiral Jesse B. Oldendorf) contained three battleships, three heavy cruisers and seven destroyers.
Air support came from Task Group 58.4, detached from the fast carrier force and containing one heavy carrier, two light carriers, two heavy cruisers, one anti-aircraft cruiser and eight destroyers. There were also three mine sweepers.
The attack would be carried out by most of the 106th Infantry Regiment (Colonel Russell A. Ayers) and the 22nd Marine Regiment Combat Team (Colonel JohnT. Walker). The two units came under the command of Tactical Group One, V Amphibious Corps (Brig. Gen. Thomas E. Watson). Watson also had the V Amphibious Corps Reconnaissance Company, Scout Company from the 4th Marine Tank Division, Company A of the 708th Amphibian Tank Battalion (with 17t LVT(A)s), 106 LVTs, 30 DUKWs and part of a demolition team. Overall the invasion force contained 7,997 men.
The eventual plan was for a series of landings on minor islands around Engebi on 17 February. The 22nd Marines would then invade Engebi on 18 February with the 106th acting as the reserve. Once Engebi was secured, the 106th (with armoured support) would land on Eniwetok. If that island was only lightly defended, then Parry was to be attacked two hours later. The date of these invasions would depend on the speed of the attack on Engebi. After the intitial fighting on Engebi it became clear that the other two islands were more strongly defended than expected, and so the plan was altered to conquer Eniwetok first and then move on to Parry.
The conquest of Engebi went fairly smoothly. The outlying islands were conquered without resistance on 17 February. The 22nd Marines landed on the lagoon coast of Engebi on the morning of 18 February, and the island was declared secure by mid-afternoon. The pre-invasion bombardment had greatly weakened the Japanese defences, and resistance was disorganised.
On 18-19 February the smaller islands between Engebi and Parry were searched and cleared. The next target was Eniwetok. This was a teardrop shaped island, with the large drop at the western end and a very long narrow tip heading east. The timetable was too tight to allow for a proper bombardment, and as a result Japanese resistance was tougher than expected. Progress was fairly slow after the initial landings on 18 February and as a result the reserves had to be committed. It took several days to reach the western and eastern ends of the island, although the fighting only cost the Americans 37 dead and 94 wounded.
The slower than expected conquest of Eniwetok meant that Parry was subjected to a longer pre-invasion bombardment. As a result when the attack finally went in on 22 February the defenders were less organised than on Eniwetok, and the island was secured in a single day.
In total the Americans lost 262 dead, 757 wounded and 77 missing during the battle for Eniwetok Atoll, while the Japanese were almost wiped out. Only 66 Japanese and Korean prisoners were taken.