They built a seaplane base on Makin and dispersed troops along the coastlines of the northern atolls to monitor the Allied forces' movement in the South Pacific.
While General Douglas MacArthur, commander of the United States Army, wanted to push towards the Philippines via New Guinea, United States Navy Admiral Chester W. Nimitz favored a drive across the Central Pacific, leapfrogging through the Gilberts, the Marshalls, the Carolines, and the Marianas, which would put American B-29 bombers within range of Tokyo.
[3] In addition to forcing the Japanese to fight two fronts against the Allies (Nimitz driving from the east and MacArthur from the south), Nimitz's plan would neutralize the outer Japanese defenses, allowing American ground, naval, and air bases to be stationed there for future attacks against other occupied island groups.
These outer islands included the atolls of Tarawa and Makin in the Gilberts, and Majuro, Kwajalein, and Eniwetok in the Marshalls.
[4] Japanese forces occupied the Gilbert Islands on 9-10 December 1941, landing troops of the South Seas Detachment on Tarawa and Makin Islands (now Butaritari and Makin),[5] a few days after the attack on Pearl Harbor, in order to protect their southeastern flank from Allied counterattacks and isolate Australia.
[9] Lieutenant Junior Grade Seizo Ishikawa, the Japanese commander in charge of defending Makin, ordered his troops to build extensive fortifications on the island.
Keiji Shibazaki had 4,836 troops, including around 2,600 Special Naval Landing Forces, 1,000 Japanese construction workers and 1,200 Korean laborers.
Without any carrier aircraft to inform him, he ordered Admiral Masami Kobayashi to disperse his 28,000 troops primarily to the outer islands of Maloelap, Wotje, Jaliuit, and Mili.
As early as November, B-24 bombers from the Seventh Air Force stationed in the Ellice Islands had flown bombing missions over Mili and Maloelap.
[2] The same day as the Majuro invasion, the 4th Marine Division under Major General Harry Schmidt began their assault on Kwajalein.
[2] Major confusion and delays were caused by poor weather and inexperienced Marines, but the pre-invasion naval and air bombardment was extremely effective.
Although the Japanese pillboxes, bunkers, and intense infantry offensives slowed the Americans, more troops, more experience in amphibious landings, effective pre-landing bombardment, and Japanese defenses on the opposite side of the atoll from where the Americans landed contributed to the capture of Kwajalein and its surrounding islands on 7 February.
On 19 February, the 106th Infantry Regiment, under Lieutenant General Thomas E. Watson, landed on the main island of Eniwetok after a heavy bombardment.
On Parry Island, the Americans used heavy gunfire support from battleships before the 22nd Marine Regiment, under Watson, waded ashore on 22 February.
The Americans used the lessons learned at Tarawa by outnumbering the enemy defenders nearly 6 to 1 with heavier firepower (including use of armor-piercing shells) after the islands took nearly a month of heavy air and naval bombardment.
[11] After the Gilberts and Marshalls were taken, the Allies built naval bases, fortifications, and airfields on the islands to prepare for an assault on the Marianas.
These islands were heavily fortified for an upcoming assault because if captured they would put American heavy bombers within range of Tokyo.