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4th Marine Division and Operation Flintlock: Baptism of Fire

Operation Flintlock was unequivocally declared a success. The U.S. Navy and Marine Corps, having absorbed the costly lessons from the Battle of Tarawa, meticulously crafted a blueprint for future amphibious operations.

February 2, 2024

Operation Flintlock, a part of Admiral Chester Nimitz's Central Pacific campaign during World War II in 1943-1944. The specific focus is on the assault on Roi-Namur in the Marshall Islands.

  1. Overview of Operation Flintlock:

    • Admiral Chester Nimitz's Central Pacific campaign gained momentum in 1943.
    • Gilbert Islands were taken in November, and the next target was the Marshall Islands.
    • Codenamed Operation Flintlock, the plan aimed to strike directly at Kwajalein Atoll.

  2. Forces and Strategy:

    • Rear Admiral Richmond Kelly Turner's V Amphibious Force led the operation.
    • Maj. Gen. Holland M. "Howlin' Mad" Smith commanded V Amphibious Corps.
    • 7th Infantry Division was chosen to secure naval facilities at Kwajalein Island.
    • 4th Marine Division, led by Maj. Gen. Harry Schmidt, would take Roi-Namur.

  3. Description of Roi-Namur:

    • Roi, a flat and barren island, had limited space, primarily hosting an airfield.
    • Namur, connected to Roi by a causeway, featured heavily forested terrain with garrison structures.
    • Occupied by Japanese forces, including Vice Admiral Michiyuki Yamada's 24th Air Flotilla.
    • Defense included various gun batteries, machine guns, blockhouses, pillboxes, antiaircraft guns, and fortifications facing north.

  4. Preparation and Bombardment:

    • A two-month bombing campaign preceded the assault.
    • Rear Admiral Richard Connoly's Task Force 53 closed in on January 29, 1944.
    • A three-day bombardment followed, delivering over 2,655 tons of high explosives.
    • Lessons from the inadequate preparatory barrage at Tarawa in November 1943 influenced the decision to thoroughly destroy defenses.

  5. Initial Objectives:

    • Five outlying islands were taken by the 25th Marines on D-day (January 31) with little trouble.
    • These islands were secured as the howitzers of the 14th Marines were positioned to support the main invasion scheduled for the following morning.

As the year 1943 neared its end, Admiral Chester Nimitz's Central Pacific campaign gathered momentum. Following the successful capture of the Gilbert Islands in November, the focus shifted to the Marshall Islands as the next strategic advancement towards Tokyo. Codenamed Operation Flintlock, the plan involved Rear Admiral Richmond Kelly Turner's V Amphibious Force, bypassing the formidable outer defenses of the Marshalls to strike directly at Kwajalein Atoll, situated at the archipelago's center. Maj. Gen. Holland M. "Howlin’ Mad” Smith, USMC, leading the V Amphibious Corps, assigned the Army’s seasoned 7th Infantry Division to secure naval facilities at Kwajalein Island in the southern group of the atoll. Simultaneously, Maj. Gen. Harry Schmidt’s untested 4th Marine Division, sailing directly from San Diego, would target Roi-Namur, including its excellent airfield located 44 miles to the north.

Roi, a flat and barren island measuring 1,200 by 1,250 yards, provided just enough space for the airfield. Connected to Roi by a 400-yard causeway and a narrow lagoon-side sand spit, Namur covered 800 by 900 yards of heavily forested terrain, offering shade to the garrison’s barracks and structures. The islands were occupied by approximately 2,000 members of Japanese Vice Admiral Michiyuki Yamada’s 24th Air Flotilla, along with a 345-strong contingent of the 61st Guard Force and potentially 1,200 service personnel. The defense of Roi-Namur included two batteries of twin-mounted 127mm guns, four 37mm cannons, 19 13.2mm heavy machine guns, and 10 20mm antiaircraft guns, primarily oriented northward in anticipation of an oceanside landing. The landscape featured eight blockhouses, 52 pillboxes, and scattered general-purpose machine guns, while antitank ditches and fighting trenches fortified the beaches.

Following a two-month bombing campaign, Rear Admiral Richard Connoly’s Task Force 53 closed in on January 29, 1944, initiating a massive three-day bombardment that delivered over 2,655 tons of high explosives. Learning from the inadequacies of the Navy’s 2.5-hour preparatory barrage at Tarawa in November 1943, which resulted in significant Marine casualties, Admiral Connoly was determined to thoroughly eliminate every man, tree, and building on Roi-Namur.

The initial objectives on D-day, January 31, were five outlying islands, secured with minimal difficulty by the 25th Marines. With these islands under control, the howitzers of the 14th Marines were strategically positioned to support the main invasion scheduled for the following morning.


In the campaign to seize control of the airfield on Roi from Japanese forces, Lt. Col. Dwight Dillon commanded the 2nd Battalion, 23rd Marines. The Marines engaged in the battle at Roi-Namur in early 1944 experienced their inaugural combat, facing their first intense military engagement.

The landings were executed by Rear Admiral Richmond K. Turner's 5th Fleet Amphibious Force and Major General Holland M. Smith's V Amphibious Corps. This corps included the 4th Marine Division under the command of Major General Harry Schmidt, the Army's 7th Infantry Division led by Major General Charles H. Corlett, as well as the 22nd Marines and the Army's 106th and 111th Infantry regiments.

The specific assignments were given to the 4th Marine Division for the capture of Roi-Namur, while the 7th Infantry Division was tasked with assaulting Kwajalein. The 2nd Battalion of the 106th had the simultaneous mission of capturing Majuro Atoll. The remainder of the 106th and the 22nd Marines were held in reserve for Kwajalein, anticipating the subsequent assault on Eniwetok three months later.

The 7th Infantry Division initiated the campaign by securing smaller islands, including Carlos, Carter, Cecil, and Carlson, on January 31. These islands served as artillery bases for the upcoming assault on Kwajalein Island. Kwajalein, being 2.5 miles long and only 880 yards wide, lacked the possibility of defense in depth. The Japanese, unaware of the capabilities of American amphibious vehicles, planned to counter-attack the landing beaches. The Southern Attack Force, supported by the battleship USS Tennessee, B-24 bombers, and artillery on Carlson island, carried out a devastating bombardment. Utilizing lessons from the Battle of Tarawa, the Navy employed armor-piercing shells and close-range firing. Landing beaches Red 1 and 2 were assaulted on February 1, with Americans reaching halfway across the runway by sunset. Despite nightly Japanese counterattacks, the island was declared secure by the fourth day.

On the north side of the atoll, the 4th Marine Division followed a similar strategy. They captured islets Ivan, Jacob, Albert, Allen, and Abraham on January 31 before landing on Roi-Namur on February 1. The capture of the airfield on the western half (Roi) was swift, while the eastern half (Namur) fell the next day. A setback occurred when a Marine demolition team inadvertently detonated a satchel charge in a Japanese bunker housing a torpedo warhead magazine, resulting in the death of 20 Marines and numerous injuries. This incident led an observation pilot to radio, "The whole damn island has blown up!"



The relatively straightforward capture of Kwajalein underscored the effectiveness of U.S. amphibious capabilities and validated the successful changes in training and tactics implemented after the costly Battle of Tarawa.  This success empowered Admiral Chester W. Nimitz, Commander in Chief, Pacific Ocean Areas, to accelerate operations in the Marshalls. Consequently, the invasion timeline included 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, recognizing the vulnerability of beach-line defenses to naval and aerial bombardment, understood the difficulty of overcoming more robust defense in depth strategies. This lesson became evident in the subsequent campaign for the Mariana Islands, where the defense in depth on Guam and Peleliu presented greater challenges compared to the relatively thin defensive line on Kwajalein.

Post-war, a pragmatic decision led to the sinking of over 150 still operational U.S. aircraft near Roi-Namur. This action proved more cost-effective than transporting the airplanes back to the U.S. mainland. The airplane graveyard included various aircraft types such as Douglas SBD Dauntless dive bombers, Vought F4U Corsairs, Grumman TBF Avengers, Curtiss SB2C Helldivers, North American B-25 Mitchells, Curtiss C-46 Commandos, and Grumman F4F Wildcats.