The US Navy Used Ulithi Atoll As Forward Base To Fight Japan In WWII

  • In September 1944, the US Navy captured Ulithi Atoll and used it to support the Allied advance.
  • The remote atoll hosted hundreds of ships for repair and rearmament and allowed troops to rest.
  • Ulithi is taking on new relevance amid heightened tensions with China in the Western Pacific.

On September 16, 1944, as US Marines began a major assault on Peleliu, Adm. William Halsey, commander of the US Navy’s 3rd Fleet, ordered III Amphibious Corps to seize Ulithi Atoll, located 400 miles to the northeast.

Seven days later, soldiers from the 81st Infantry Division began landing on Ulithi’s coral islets. The Japanese had abandoned the atoll a few months earlier, and the US landing was unopposed. Within two days the Americans had completed their initial unloading operations.

Located roughly between Guam and Palau and some 1,300 miles from Tokyo, Ulithi would have been easy to overlook, but within a few weeks it would become essential to the war effort.

Hundreds of Allied ships would fill its lagoon and thousands of troops would occupy its islands. The remote coral outcropping would allow them to take the fight all the way to Japan’s shores.

The world’s largest naval facility

Navy ships at Ulithi Atoll

Sorlen Island and the north anchorage at Ulithi Atoll in late 1944.

US Navy



Ulithi is made up of 40 small islands, only four of which are inhabited, in an oblong ring around a lagoon of some 200 square miles in size and depths of 80 feet to 100 feet.

The atoll was spotted by US Pacific Fleet commander Adm. Chester Nimitz while looking over a map of the area to find a good location for an advance base to support future operations against the Philippines and Japan.

The Japanese had a weather station on the atoll and made limited use of its lagoon as a fleet anchorage and seaplane base earlier in the war, but they withdrew after coming under attack from US carrier aircraft. The Japanese saw no strategic value in Ulithi and did not think it could be used against them.

US naval construction battalions, known as “Seabees,” quickly proved them wrong, setting up Ulithi as an advance base almost immediately after landing in late September 1944.

Navy sailors at Mogmog island in Ulithi atoll

US Navy sailors on Mogmog Island in November 1944.

US Navy/Charles Fenno Jacobs



The Seabees lengthened an abandoned airstrip on Falalop Island to 1,200 yards, set up buoys to designate areas in the lagoon where ships could anchor, established a headquarters on Asor Island, and built a boat pool and 100-bed hospital on Sorlen Island.

The Navy also transferred Ulithi’s native population to one of the smaller islands, where they lived for the rest of the war.

Mogmog, the largest and most habitable island, became a badly needed haven for US troops. It had ball fields, a band stand, a chapel, and a 1,200-seat theater. There was also an ice cream barge that could make 500 gallons of ice cream in one shift. At its peak, the island hosted 20,000 men, with roughly 9,000 there on any given day.

The lagoon was Ulithi’s most valuable feature. Hundreds of ships, including entire carrier groups, anchored in its waters, alongside dozens of seaplanes. There they would be tended to by the small army of Navy engineers and logistics personnel assigned to Service Squadron 10.

Navy aircraft carrier USS Randolph kamikaze damage

USS Randolph alongside repair ship USS Jason at Ulithi Atoll on March 13, 1945. Randolph was hit by a Japanese kamikaze on March 11.

US Navy



Service Squadron 10 oversaw the rearming, resupplying, and repairing of Navy ships and aircraft, and otherwise supported the war effort’s logistical needs.

In all, the unit had over 400 vessels, including repair ships, tankers, floating dry docks, crane ships, desalination ships, tugs, floating barracks, and floating workshops.

The ships and sailors of Service Squadron 10 allowed the Navy to continue fighting across the vast Pacific expanse. They were called Nimitz’s “secret weapon.”

Ulithi became an extremely important base of operations. Any ship could be repaired — or mended enough to get back to a bigger base — and rearmed there and troops could rest and recuperate. Aircraft carriers moored there could continue launching rescue, reconnaissance, and bombing operations.

The liberation of the Philippines and the invasions of Iwo Jima and Okinawa were all launched from Ulithi. It also hosted preparations for the planned invasion of Japan’s home islands.

USS Mississinewa sinks at Ulithi

USS Mississinewa after being hit by a Japanese Kaiten manned torpedo on November 20, 1944.

US Navy



By the end of the war, Ulithi was the world’s largest naval facility, hosting as many as 617 vessels. The presence of so many ships also made Ulithi a target.

The Japanese repeatedly tried to attack it with aircraft, mini-subs, and even Kaiten manned torpedoes. On November 20, 1944, the Japanese sank the fleet oiler USS Mississinewa, killing some 63 sailors and officers.

On March 11, 1945, a long-range kamikaze plane struck the carrier USS Randolph, killing 25 men and wounding 106 more. Randolph was repaired at Ulithi and joined the invasion of Okinawa a month later.

Japan even sent its enormous plane-carrying I-400-class submarines to attack Ulithi. The subs were en route when Japan surrendered and had to return.

Newfound relevance

US hospital ship USNS Mercy near Ulithi Atoll

US military hospital ship USNS Mercy near Ulithi Atoll in March 2018.

US NavyMCS2 Kelsey L. Adams



Ulithi was largely abandoned after the war, but the atoll is taking on new relevance as heightened tensions with China make another war in the Pacific more likely.

A forward base would be invaluable in such a conflict, especially since modern guided-missile warships cannot be rearmed while at sea.

The need for such a base is compounded by the fact that the US Navy would likely struggle to repair warships damaged in battle with great-power rivals like China or Russia, according to a Government Accountability Office report released last year.

Falalop Island in Ulithi Atoll

An airfield and a high school damaged by Typhoon Maysak on Falalop Island in Ulithi Atoll in December 2015.

US Air Force/Osakabe Yasuo



The complexity of modern warship design coupled with US divestment of naval repair assets and the closure of many public shipyards after the Cold War make fixing battle-damaged ships more challenging.

The US Navy is already struggling with a repair backlog. Its surface ships currently face roughly 4,200 days of maintenance delays — effectively reducing the fleet by about 10 ships a year, Navy officials said this month.

With China continuing to build ships, expand the reach of its missile arsenal, and muster industrial capacity three times that of the US, the Navy would need every advantage it could get.

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