extent of such fortifications was unknown. Japan regarded them as part of the "outer ring" of their territory. The strategic importance of the Marshalls had been recognized as early as 1921 in Plan Orange, an American interwar plan for a possible conflict with Japan. The Marshalls were a key step in the island-hopping march to the Japanese mainland. After losing the Solomon Islands and New Guinea to the Allies in 1943, the Japanese command decided that the Gilbert and Marshall Islands were expendable. They preferred fighting a decisive battle closer to home. Nevertheless, 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 he had very few 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 had his men spread out over a very wide area, with IJN air bases located on Roi-Namur, Mili, Maloelap, Enewetak, 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. The Japanese had twin 12.7 cm guns on each end of the island plus 80mm guns on the ocean and lagoon sides. The 22nd Air Flotilla, depleted after the Gilbert campaign, had 128 aircraft in the Marshalls, 10 on Kwajalein. 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 further 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 all Japanese aircraft. 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, Consolidated B-24 Liberators bombed strategic targets. In the beginning, the most important was Mili, the Japanese base closest to the Gilberts and