The Gilbert and Marshall Islands campaign marked a significant chapter in the Pacific theatre of World War II, with a series of battles spanning from August 1942 to February 1944. Led by the United States Pacific Fleet and Marine Corps, the primary objective was to establish airfields and naval bases, vital for air and naval support operations across the Central Pacific. Under the code names Operation Galvanic, Kourbash, Flintlock and Catchpole, the campaign involved seizing control of strategic locations such as Tarawa, Makin, Kwajalein, Eniwetok and Majuro. The fiercely fought battles during the Battle of Tarawa on 20–23 November and the Battle of Makin on 20–24 November 1943 were particularly significant, with several military tactics and warfare strategies employed. The successful seizing of these islands allowed the United States to establish a firm foothold in the Central Pacific, paving the way for further missions and ultimately, contributing to the outcome of the overall Pacific theatre of World War II.

The Battle of Kwajalein was fought between January 31st and February 3rd, 1944, on Kwajalein Atoll in the Marshall Islands. The United States deployed a twin assault on the main islands of Kwajalein in the south and Roi-Namur in the north, employing the lessons learned from the aftermath of the Battle of Tarawa. The Japanese defenders put up a fierce resistance despite being under-prepared and outnumbered. Although the determined defense of Roi-Namur left only 51 survivors of an original garrison of 3,500, the battle represented a key victory for the U.S. and was critical for its island-hopping march to Japan.

The United States forces for the landings were Rear Admiral Richmond K. Turner's 5th Fleet Amphibious Force and Major General Holland M. Smith's V Amphibious Corps. The 4th Marine Division, commanded by Major General Harry Schmidt, was assigned to Roi-Namur, while the 7th Infantry Division, commanded by Major General Charles H. Corlett, would make the assault on Kwajalein. Additionally, the 22nd Marines and the Army's 106th and 111th Infantry regiments were also deployed.

On January 30, 1944, the United States launched a massive air and naval bombardment, which lasted for two months, against the Marshall Islands. The operation was part of the Allied forces' island-hopping strategy to capture strategic locations in the Pacific and bring the war closer to Japan. The U.S. forces comprised of an impressive 85,000-man amphibious assault force and around 300 warships.

Carlos, Carter, Cecil, and Carlson were small islands that were captured on January 31st, and were used as artillery bases for the next day's assault. Kwajalein Island, at 2.5 miles long, was only 880 yd wide, leaving no possibility for defense in depth. The Japanese had planned a counter-attack of the landing beaches, but 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. Consequently, the strongest defenses on Kwajalein faced the ocean. The bombardment by the Southern Attack Force, including the battleship USS Tennessee, and B-24 bombers was devastating, and the Navy had changed its bombardment tactics based on the Tarawa experience. It used armor-piercing shells as well as firing into the island at closer ranges.

Top photo: Marines regroup and reorganize at the shoreline. Kwajalein USMC Photo No. K-9. From the Frederick R. Findtner Collection (COLL/3890), Marine Corps Archives & Special Collections. OFFICIAL USMC PHOTOGRAPH. Click to enlarge.

Middle photo: Marine infantry fighting their way inland amidst damaged concrete supports. Kwajalein USMC Photo No. K-4. From the Frederick R. Findtner Collection (COLL/3890), Marine Corps Archives & Special Collections. OFFICIAL USMC PHOTOGRAPH. Click to enlarge.

Bottom photo: Japanese prisoner minus his uniform. He appears to be pointing in the direciton of more Japanese soldiers. Kwajalein USMC Photo No. K-15. From the Frederick R. Findtner Collection (COLL/3890), Marine Corps Archives & Special Collections. OFFICIAL USMC PHOTOGRAPH. Click to enlarge.

Photo album: The Battle of Kwajalein from the Marine Corps Archives & Special Collections

The official U.S. Army history of the battle quotes a soldier as saying "the entire island looked as if it had been picked up 20,000 feet and then dropped." Landing beaches Red 1 and 2 were assaulted at 09:30 on February 1st, and the Americans reached halfway across the runway by sunset. The Japanese counterattacked every night, but the island was declared secure by the end of the fourth day.

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 January 31st, and then landing on Roi-Namur on February 1st. The airfield on the western half (Roi) was captured quickly, and the eastern half (Namur) fell the next day. 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.

On February 1, the 7th Infantry Division landed on Kwajalein Island, while the 4th Marine Division set foot on the twin islands of Roi and Namur. The Japanese, though greatly outnumbered, decided to fight until the bitter end. However, the U.S. forces proved to be a formidable opponent, as they quickly secured Roi and Namur on the first and second day of the assault, respectively. The Battle of Kwajalein, on the other hand, lasted for three strenuous days, with the 7th Infantry relentlessly pounding the Japanese garrison until they declared the island secure on February 4.

Despite the challenges, the Allies successfully accomplished the capture of Kwajalein, which was ahead of Nimitz's expectations. This achievement enabled them to advance by 60 days the planned attack on Eniwetok, which was 400 miles northwest of Kwajalein. This attack was of strategic significance since the Allied forces needed to inflict damage on Japan's fleet. The assault destroyed 275 Japanese aircraft and sank nearly 40 ships. The fight for Eniwetok lasted for five grueling days, but the results were favorable as the island fell on February 21. 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. It allowed Admiral Chester W. Nimitz, Commander in Chief, Pacific Ocean Areas, to speed up operations in the Marshalls and invade Ebeye Island on 3–4 February, Engebi Island on 18–19 February, Eniwetok Island on 19–21 February, and Parry Island on 22–23 February.

The Japanese also realized that beach-line defenses were too vulnerable to naval and aerial bombardment. 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.

The Battle of Kwajalein was a significant morale victory for the United States, as it represented the first time the Americans had penetrated the "outer ring" of the Japanese Pacific sphere. For the Japanese, it signified the failure of the beach-line defense and their realization that their economic and political assets could be seriously compromised if their sea lanes were overrun. The U.S. victory in the Marshalls came with a heavy cost for the Japanese. Over 3,500 Japanese defenders were killed, and roughly 200 were captured on Roi and Namur. Meanwhile, on Kwajalein, almost 5,000 Japanese soldiers were killed, and only a handful were captured. The U.S. also suffered casualties, with 177 soldiers killed and 1,000 wounded on Kwajalein.

The successes of the U.S. forces in the Marshalls provided them with a significant anchorage point and staging area. These resources were critical in the continuation of their amphibious operations in the central Pacific, including the Mariana Islands. The Allied victory also intensified the isolation of the remaining Japanese island outposts, which had not been targeted in their island-hopping campaign. These outposts included Wake Island, one of the first islands captured by Japan in the early days of the war.

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