Amphibious Assault

Key to the WWII Battle for Peleliu

After the U.S. entered World War II (WWII) in 1941, military planners quickly developed an island-hopping strategy for a westward push across the Pacific to the Japanese home islands. By the fall of 1944, after the successful capture of the Marianas Islands, the next target was the Palauan chain in the Caroline Islands. Operation Stalemate II, the invasion of Palau, was the last major obstacle to the Philippines and Peleliu was the key (Figure 1).

Figure 1: The two-pronged battle plan to the Japanese home islands went through Palau to the Philippines. Major battles indicated in red. Image courtesy of the National Park Service.

To achieve success against well-fortified islands required an unprecedented level of coordination between the U.S. Navy, Marines, and Army. It also required a completely new way of thinking, new equipment designed specifically for the task (amphibious craft), and a specially trained team of men. The new strategy was predicated on getting the maximum number of men safely on shore as quickly as possible. In the case of Peleliu, it was to get 4,500 Marines ashore in the first 19 minutes of the assault, paving the way for the remaining 24,000 to land within 90 minutes.

Amphibious Strategy and Planning

The complex technique devised for putting men ashore on an enemy-held coast fringed by a reef and lagoon involved hard lessons learned. From Tarawa, the amphibious landing force stalled getting across the reef because of unknown obstacles. From Guam and Makin, forcing men to wade from the reef edge across an exposed lagoon raked with enfilading fire cost many lives. Those mistakes were not to be repeated at Peleliu.

Figure 2: The first wave of LVT(A)s move toward the invasion beaches, passing through the inshore bombardment line of LCI gunboats, 15 September 1944. Cruisers and battleships are bombarding from the distance. The landing area is hidden by dust and smoke. Photographed from a USS Honolulu (CL-48) plane. Source: NARA 80-G-283533.

The new plan involved five imaginary parallel lines offshore where various elements of the task force could stage with their ships and troops before the assault. Farthest out at 18,000 yards were the big ships and transports. Next came the LSTs (landing ship transports) carrying the troops in LVTs (landing vehicle tracked) in their cavernous holds. At 6,000 yards from shore, the LSTs opened their bow doors and the small LVTs (sometimes called amtracs) embarked. The fourth line was 4,000 yards from shore, still 30 minutes travel time to the beach. This was the rendezvous line for all of the assault waves to form groups opposite their designated beaches. The final line before the reef was at 2,000 yards and 15 minutes from shore, where the amtracs returned after carrying the assault waves to the beach and where the next groups of men and supplies transferred from small boats to the amtracs. When the troop-carrying amphibious fleet reached the last line at 1,000 yards, they were on their own to cross the reef and get to shore.

Stewarding the small fleet at each line were submarine chasers, patrol craft, and Higgins boats, hoisting signaling flags, forming up the waves, and in constant radio contact. Preceding the first waves of personnel were armored LVT(A)s (amphibian tanks) armed with machine guns and howitzers, to neutralize beach defenses and support the landings. LCI(G) (landing craft, infantry, gunboats) armed with rockets stood offshore at the 1,000-yard line and raked defensive positions and provided covering fire for the LVT(A)s. Overhead, naval gunfire pummeled the island and aircraft bombed and strafed. The landing was a complex maneuver requiring precise timing and coordination.

Frogmen: The Role of UDTs

As careful as the plan was, unless the amphibious craft could get over the reef; avoid the mines; navigate the concrete anti-boat obstacles, the coral heads, and boulders; and land on shore, it was doomed to failure. The Navy underwater demolition teams (UDTs) were formed in 1942 in response to this fundamental problem. However, it was not until the near failure of the landing at Tarawa that their importance was recognized. From that point forward, UDT reconnaissance was integral to all planning.

Figure 3: Andy Anderson, GM1/c, of UDT7, with a J-13 mine at Peleliu. This type of ‘horned’ mine was particularly dangerous because it was so unstable. Source: Navy Seal Museum, 2002.0034.12.

In the run up to the Peleliu operation, UDT 10 scouted the invasion beaches in USS Burrfish. The information gathered in August 1944 revealed an array of concrete tetrahedrons, a double row of wooden posts 75 yards from shore, barbed wire, horned mines and, importantly, in some areas the reef was awash with barely two feet of water at low tide. Three days before D-Day, UDTs 6 and 7 deployed along the invasion beaches to destroy obstacles, but more critically, to blast wide ramps into the coral for the amphibious craft. Not only was their mission dangerous and in broad daylight, naval fire support from offshore flew overhead and periodic sniper and machine gun fire from shore targeted the unarmed swimmers in the shallow lagoon. The night before the assault, UDTs crawled ashore to demolish rock cribs, posts, barbed wire, concrete cubes, and set buoys off the reef to mark the newly blasted passageways.


The Peleliu amphibious assault and the role of the UDTs marked a turning point in amphibious military doctrine. Unquestionably, it saved lives, but it did not prevent the loss of others and the heavy loss of equipment crossing the reef and lagoon during the first hours. The battle started well offshore and the battlefield includes the reef and lagoon, the focus of this project. The successful capture of Peleliu and nearby Angaur paved the way for the final push toward the Philippines and Okinawa.