Employing the hard-learned lessons of the Battle of Tarawa, the United States launched a successful twin assault on the main islands of Kwajalein in the south and Roi-Namur in the north.

For the US, the battle represented both the next step in its island-hopping march to Japan and a significant morale victory because it was the first time the Americans had penetrated the "outer ring" of the Japanese Pacific sphere.

Its facilities were being utilized as outlying bases for submarines and surface warships, as well as for air staging for future advances being planned against Ellice, the Fiji Islands, and Samoa.

[1]: 31  Akiyama had his men spread out over a very wide area, with naval-air bases located on Roi-Namur, Mili, Maloelap, Enewetak, and Wotje.

On 18 December renewed strikes were initiated against enemy targets on Mili with land-based Douglas A-24 Banshee dive bombers and Bell P-39 Airacobra fighters making their debut in the Marshall air offensive.

The 7th Infantry Division began by capturing the small islands labeled Carlos, Carter, Cecil, and Carlson on 31 January, which were used as artillery bases for the next day's assault.

[1]: 33  They had not realized until the Battle of Tarawa that American amphibious vehicles could cross coral reefs and land on the lagoon side of an atoll; accordingly the strongest defenses on Kwajalein faced the ocean.

[1]: 33  The bombardment by the Southern Attack Force, including the battleship USS Tennessee,[1]: 44, 54  plus B-24 bombers from Abemama and artillery on Carlson island was devastating.

The Navy had changed its bombardment tactics based on the Tarawa experience and used armor-piercing shells as well as firing into the island at closer ranges.

[1]: 66 On the north side of the atoll, the 4th Marine Division followed a similar plan, first capturing islets Ivan, Jacob, Albert, Allen, and Abraham on 31 January, and then landing on Roi-Namur on 1 February.

The worst setback came when a Marine demolition team threw a satchel charge of high explosives into a Japanese bunker, not realizing it was a torpedo warhead magazine.

The resulting explosion killed 20 Marines and wounded dozens more[2] and caused an observation pilot to radio, "The whole damn island has blown up!

"[3] The relatively easy capture of Kwajalein demonstrated US amphibious capabilities and showed that the changes to training and tactics after the costly Battle of Tarawa had been effective.

In the campaign for the Mariana Islands, the defense in depth on Guam and Peleliu would be much harder to overcome than the comparatively thin line on Kwajalein.