The Marshall Islands Campaign (31 January-22 February 1944) was the first time that the Americans captured pre-war Japanese territory, and was made up of two main parts - Operation Flintlock, the conquest of Kwajalein and Operation Catchpole, the conquest of Eniwetok.
The invasion of the Marshall Islands was one of the earlier American war aims in the Pacific, but it soon became clear than the existing Allied bases were too far from the islands. In order to gain bases nearer to the Marshalls, the Americans invaded the Gilbert Islands, leading to the battles of Makin and Tarawa.
The Marshall Islands consist of 32 island groups, split into two main chains. The north-eastern chain is known as Ratak, or sunrise, while the south-western chain is called Ralik, or sunset. The two chains were around 100 miles apart, and run north-west to south-east for several hundred miles. The largest atolls in the Ratak chain are Mille, Maloelap and Wotje, while Jaluit, Kwajalein, Rogelap, Bikini and Eniwetok are the main atolls on the Ralik chain. Most of the islands are low lying coral reefs formed into atolls, including some of the largest in the world. The Marshall Islands had been part of the Spanish Empire until the aftermath of the Spanish-American War, when they were sold to Germany. They were then conquered by Japanese during the First World War, and became a Japanese mandate after the war.
In August 1943 Admiral Nimitz asked the Joint Chiefs of Staff to give him official orders to invade the Marshalls. On 1 September they responded with an order to him to seize and control the Marshalls, and at the end of the operation to have seized or controlled Wake, Eniwetok and Kusaie (the eastern-most of the Caroline Islands). The operation had four official aims - to prepare to gain control of the Carolines, to inflict loses on the enemy, to improve the security of the lines of communication and to support operations in the Pacific and Indian Oceans. At this stage the invasion was to begin on 1 January 1944 (or when allowed by the campaign in the Gilberts). The 4th Marine Division, 22nd Marine Regiment (reinforced) and 7th Infantry Division were allocated to the invasion at this point.
The original plan was to invade Wotje, Maloelap and Kwajalein at the same time, in order to knock out two thirds of the Japanese air force in the islands. Most of the other airfields, mainly on Jaluit and Mille, could be neutralized from those islands. Nimitz then suggested bypassing Wotje and Malolap,and focusing on Kwajalein, in the centre of the Marshalls. Although this plan was opposed by most of his subordinates, Nimitz got his way and the new plan was confirmed on 14 December 1943. The invasion was now scheduled for 31 January 1943. On 26 December, at the request of Admiral Spruance, Majuro, at the eastern end of the Marshalls, was added as an objective.
The Japanese had airfields on several of the islands. The most dangerous during the invasion of the Gilbert Islands was on Mille, simply because it was the nearest to them. Maloelap posed the biggest threat to operations within the Marshals, as there was a large and well defended airfield on Taroa, the largest island in the atoll. Roi Island was almost entirely dominated by the airfield built there. Wotje was a major Japanese base, again with an airfield.
The islands came under heavy and persistence air attack by long range B-24s, and later by aircraft based on Tawara and Makin. They were also subjected to one major naval air attack on 4 December, but this was cut short after it became clear that the Japanese defenders still had teeth - one carrier was even hit by a torpedo, although survived.
D-Day for Operation Flintlock was 31 January. This saw a long series of smaller islands around Kwajalein and Roi-Namur captured (including Carlson, Carlos, Carter, Cecil and Chauncey). Majuro Atoll was also occupied, this time without any resistance.
The three main invasions were then launched on 1 February. General Holland Smith's 5 Amphibious Corps attacked Kwajalein Atoll in the middle of the islands while General Harry Schmidt's 4th Marine Division landed on Roi and Namur, 45 miles to the north-west.
None of the Japanese garrisons held out for long. Roi was taken on 1 February. Namur was secured by noon of 2 February. Between them these two attacks cost the Americans 190 dead and 547 wounded, while the Japanese lost 3,500 dead and 264 captured. The fighting on Kwajalein lasted a little longer, but the island was secured by 4 February. This time the Americans lost 177 dead and 1,000 wounded, the Japanese 3,800 killed.
These quick conquests convinced Admiral Nimitz to bring Operation Catchpole - the invasion of Eniwetok, 400 miles to the north-west, forward by two months. On 18 February General John Walker's 22nd Marine Regiment landed on Engebi. On 19 February the 106th Regiment, 27th Infantry (General Thomas Walker) landed on Eniwetok. Once again the battle was short, and the island was secured by 21 February. Finally, Parry Island was conquered on 22 February, after a single day of fighting against what was meant to be the strongest garrison in the group.
In the aftermath of these battles most of the smaller atolls in the Marshalls were conquered, mainly without any fighting. The only exceptions were Wotje, Mille, Jaluit and Maloelap, which were left alone and allowed to wither on the vine for the rest of the war.
The Americans soon turned the Marshall Islands into a major air and naval base. An airfield was built on Dalap Island (Majuro), and was used to raid to the remaining Japanese held islands. The Navy also built a fleet anchorage and medical facilities.
The Japanese airfield on Roi was repaired and enlarged. It was soon in regular use, and was officially commissioned on 15 May.
The airfield on Kwajalein Island was soon turned into a 6,300ft heavy bomber field. Naval facilities were also built on the island. This airfield was used for the USAAF raids on Truk.
The airstrip on Engebi in Eniwetok was ready to take three B-25 squadrons by 5 March. A 6,000ft field on Eniwetok Island was completed by 20 March. Eniwetok was also used as a fleet anchorage.
The bases in the Marshalls were used to secure American communications in the area, but also as a base for attacks on the Mariana Islands, the first position within the inner ring of Japanese defences to be attacked.