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What made the Marshall Islands Operation America's first breakthrough of Japan's Pacific fortress? Between November 1943 and March 1944, Operations Flintlock and Catchpole shattered Japan's outer defensive ring through revolutionary amphibious warfare. This pivotal campaign earned veterans the Asia-Pacific Theater campaign star while demonstrating tactics that would win the Pacific War.
The Marshall Islands Operation (November 26, 1943 – March 2, 1944) marked America's first penetration of Japan's outer defensive ring in the Pacific, comprising Operations Flintlock and Catchpole. This largest amphibious assault of the war to date demonstrated revolutionary amphibious warfare tactics while establishing crucial bases for the subsequent Mariana Islands campaign.
Admiral Chester W. Nimitz organized the Marshall Islands Operation as part of a two-pronged Central Pacific offensive. Following the costly lessons of Tarawa in November 1943, American strategists sought to establish airfields and naval bases that would support future operations across the Central Pacific while taking pressure off General MacArthur's Southwest Pacific campaigns.
After the Gilbert Islands fell to American forces in late November 1943, Admiral Mineichi Koga of the Japanese Combined Fleet found himself uncertain of American intentions. Without carrier aircraft for reconnaissance, he ordered Admiral Masami Kobayashi to disperse his 28,000 troops primarily to the outer islands of Maloelap, Wotje, Jaluit, and Mili. However, Allied intelligence intercepted and decrypted Japanese transmissions, revealing which islands were more heavily defended.
American codebreakers proved decisive in shaping the invasion strategy. Instead of attacking the heavily fortified outer islands as the Japanese expected, U.S. forces would bypass these positions and strike directly at the strategically important but lesser-defended islands of Majuro, Kwajalein, and Eniwetok.
|
Command Level |
Commander |
Unit |
Strength |
|
Overall Command |
Admiral Chester W. Nimitz |
CinCPac/CinCPOA |
Fleet Command |
|
Fifth Fleet |
Vice Admiral Raymond A. Spruance |
Task Force 50 |
297 ships |
|
Joint Expeditionary Force |
Rear Admiral Richmond K. Turner |
Task Force 51 |
54,000 troops |
|
Southern Attack Force |
Rear Admiral Turner |
Task Force 52 |
7th Infantry Division |
|
Northern Attack Force |
Rear Admiral Richard L. Conolly |
Task Force 53 |
4th Marine Division |
|
Reserve Force |
Rear Admiral Harry W. Hill |
Task Group 51.1 |
22nd Marines |
The joint expeditionary force included 297 ships (not counting carrier task forces or submarines) and 54,000 Marine and Army assault troops. Vice Admiral Raymond A. Spruance commanded the Fifth Fleet from the heavy cruiser Indianapolis, while Rear Admiral Richmond K. Turner commanded the Joint Expeditionary Force from the amphibious command ship Rocky Mount.
Vice Admiral Marc Mitscher's Fast Carrier Task Force provided air cover with six fleet carriers and six light carriers, escorted by eight battleships and a full complement of cruisers and destroyers. The Southern Attack Group was supported by the old battleships New Mexico, Mississippi, Idaho, and Pennsylvania, along with heavy cruisers, light cruisers, destroyers, and escort carriers.
Key Naval Vessels by Class:
Pre-Invasion Air Campaign
Beginning on January 27, 1944, Mitscher's Fast Carrier Force began systematic attacks on Japanese airfields in the Marshalls. Armed with detailed photo intelligence and precise strike plans, these strikes proved far more effective than previous raids. The Japanese had approximately 150 operational aircraft in the Marshalls on January 27; by D-Day on January 31, there were none remaining.
On January 31, 1944, Rear Admiral Harry W. Hill dispatched the V Amphibious Corps Reconnaissance Company and the 2nd Battalion, 106th Infantry, 27th Infantry Division to land on Majuro. The atoll was taken without any U.S. casualties, as the Japanese had largely abandoned it over a year earlier, leaving only minimal forces behind.
At Rear Admiral Carl Moore's suggestion, Majuro atoll had been added to Operation Flintlock's objectives because its deep lagoon would provide the ships of the 5th Fleet with a safe anchorage for refueling, resupply, and repairs. Airfields built on Majuro would also protect the supply line to Kwajalein against attacks from isolated Japanese garrisons.
Rear Admiral Monzo Akiyama commanded the Kwajalein garrison of approximately 8,000 men, though only about half were combat-capable soldiers; the remainder consisted of Korean laborers and aviation personnel. The Japanese had twin 12.7 cm guns on each end of the island plus 80mm guns on the ocean and lagoon sides. The defense system was mostly linear with little depth.
The American plan called for simultaneous attacks on opposite ends of the 44-mile-long Kwajalein Atoll. Major General Charles H. Corlett's 7th Infantry Division would assault Kwajalein Island in the south, while Major General Harry Schmidt's 4th Marine Division would attack Roi and Namur islands in the north.
In the pre-dawn hours, soldiers of the 7th Infantry Division's Cavalry Reconnaissance Troop and Company B, 111th Infantry paddled ashore in rubber boats to seize Cecil, Carter, Carlson, and Carlos islands. This allowed the establishment of artillery bases on Carlson with five artillery battalions, providing fire support for the main landings just two miles away.
The preliminary bombardment began at 0700 hours on February 1, 1944. Several battleships, cruisers, and a dozen destroyers fired 7,000 rounds of high explosive and armor-piercing shells at Japanese fortifications on the invasion beaches. The bombardment proved devastatingly effective, with engineers finding only one intact pillbox on the beach.
Despite the intensity of pre-invasion barrage, Japanese defenders engaged lead troops with mortars and light machine gun fire. Soldiers landed in Landing Vehicle, Tracked (LVTs), landing craft infantry (LCIs), and amphibious utility craft known as "Ducks." M-4 medium tanks equipped with snorkeling gear landed with the fifth wave, providing direct fire support with their 75mm cannons.
As Americans advanced over Kwajalein, Japanese forces countered with fierce infantry charges backed by strong bunkers and pillboxes. By February 2, only 1,500 of the original 5,000-man Japanese garrison remained alive. When the island was declared secure, only 265 Japanese survived as prisoners, while American casualties totaled one killed for every 100 Japanese eliminated.
The 4th Marine Division's assault on Roi-Namur faced 345 naval infantry of the 61st Naval Guard Force, 1,655 naval airmen, and 600 laborers under Rear Admiral Michiyuki Yamada. The attack was initially confused, but the airfield on Roi was captured quickly, with Namur falling the following day.
Originally planned for May 1944, the Eniwetok operation was accelerated when it became clear that reserve forces wouldn't be needed at Kwajalein. On February 2, Admiral Nimitz asked Admiral Spruance for his thoughts on an early invasion. Spruance agreed, and Admiral Hill, fresh from the unopposed Majuro operation, was given command on February 3.
When the Gilbert Islands fell in late 1943, the Imperial Japanese Army assigned defense of Eniwetok to the 1st Amphibious Brigade under Major General Yoshimi Nishida. The brigade originally consisted of 3,940 men formed from reservists of the 3rd Independent Garrison in Manchukuo. However, after their supply ship Aikoku Maru was sunk during Operation Hailstone, only 2,586 men reached Eniwetok.
Japanese Weapons and Equipment at Eniwetok:
The invasion of Eniwetok began February 17, 1944, commanded by Rear Admiral Harry W. Hill with Colonel John T. Walker commanding the landing Marines. The plan called for taking the atoll in four stages: invasion of islets adjoining Engebi, then Engebi itself, followed by Eniwetok and Parry islands.
Phase One: Engebi Island (February 17-18)
The 22nd Marines landed on the lagoon coast of Engebi on the morning of February 18, following the capture of outlying islands on February 17. The island was declared secure by mid-afternoon, though the conquest revealed that the other two main islands were more heavily defended than expected.
Phase Two: Eniwetok Island (February 19-21)
Originally planned as a simultaneous assault with Parry Island, the plan was modified after Engebi's capture revealed stronger defenses elsewhere. The 106th Infantry used two battalions to attack Yellow Beaches 1 and 2 on the lagoon side, supported by the 2nd Separate Tank Battalion (Marine).
Phase Three: Parry Island (February 22)
The final assault on February 22 involved the battleships Tennessee and Pennsylvania, heavy cruisers Indianapolis and Louisville, and destroyer Hailey delivering more than 900 tons of explosives onto Parry Island. The 1st and 2nd Battalions of the 22nd Marines conducted the landing at 0900 hours, advancing rapidly with tank support.
Battleship Main Batteries:
Close Support Weapons:
Japanese defenses relied primarily on coastal artillery and prepared positions. The defense system on most islands was linear with little depth, featuring twin 12.7 cm guns on each end of major islands plus 80mm guns covering both ocean and lagoon approaches.
Fortification Types:
The Seventh Air Force played a crucial role with B-24 Liberator bombers staging through Baker Island airfield. Other aircraft participating included B-25 Mitchell bombers, A-24 Banshee dive bombers, P-39 Airacobra fighters, and P-40 Warhawk fighters.
Carrier-Based Aircraft:
The 22nd Air Flotilla had been depleted after the Gilbert campaign, with only 128 aircraft remaining in the Marshalls and just 10 on Kwajalein. By D-Day, American carrier strikes had destroyed all remaining Japanese aircraft in the islands.
|
Operation |
Killed |
Wounded |
Missing |
Total |
|
Kwajalein |
348 |
1,462 |
183 |
1,993 |
|
Eniwetok |
262 |
757 |
77 |
1,096 |
|
Total |
610 |
2,219 |
260 |
3,089 |
Of approximately 8,000 Japanese troops defending Majuro and Kwajalein, only 253 were taken prisoner. At Eniwetok, only 66 Japanese and Korean prisoners were captured from the entire garrison.
The quick seizure of the Marshall Islands allowed Admiral Nimitz to advance the Marianas invasion date by almost six months. Japanese preparation time for defending islands like Saipan and Tinian was shortened, while U.S. units that participated in the Marshalls remained relatively intact for subsequent operations.
The Marshall Islands campaign demonstrated the soundness of American amphibious doctrine and provided crucial experience for larger operations. Two critical lessons involved continuous close air support and naval gunfire support, which became standard for all subsequent Pacific operations.
For the United States, the Marshall Islands campaign represented both the next step in the island-hopping advance toward Japan and a significant morale victory, marking the first penetration of Japan's "outer ring" of Pacific defenses.
Veterans who served in the Marshall Islands Operation between November 26, 1943, and March 2, 1944, were eligible for the Asia-Pacific Theater campaign star on their Pacific Theater ribbon. This included personnel who participated in:
The Marshall Islands Operation marked a turning point in Pacific warfare, proving that American forces could successfully conduct large-scale amphibious operations against defended objectives. The campaign's success led directly to the accelerated timeline for subsequent operations and demonstrated the effectiveness of the Central Pacific strategy in bringing the war closer to Japan's home islands.
Sources and References
Primary Sources:
Official Military Records:
Secondary Sources:
Additional Reading:
