On September 16, 1944, the commander of the US Navy's 3rd Fleet ordered the III Amphibious Corps to seize Ulithi atoll.

Soldiers from the 81st Infantry Division landed on Ulithi's coral islets. The US landed without a hitch after the Japanese abandoned the atoll. The Americans finished their unloading operations within two days.

It would have been easy to overlook Ulithi, but within a few weeks it would be crucial to the war effort.

The lagoon would be filled with hundreds of Allied ships. They could 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 200 square miles.

The atoll was spotted by the US Pacific Fleet commander as he looked over a map to find a good location for an advance base.

The Japanese had a weather station on the atoll but withdrew after being attacked by the US. The Japanese didn't believe that Ulithi could be used against them.

Ulithi was set up as an advance base by the Seabees almost immediately after they landed.

Navy sailors at Mogmog island in Ulithi atoll
US Navy sailors on Mogmog Island in November 1944.
US Navy/Charles Fenno Jacobs

The Seabees built a hospital on Sorlen Island, set up a headquarters on Asor Island, and shortened an abandoned airfield on Falalop Island.

The native population of Ulithi was moved to one of the smaller islands where they lived for the rest of the war.

The biggest island in the world, Mogmog, became a good place for US troops to stay. There was a band stand, a chapel, and a 1,200 seat theater. 500 gallons of ice cream can be made in one shift. There were 20,000 men on the island at one point.

The most important feature was the lagoon. Dozens of seaplanes and hundreds of ships anchor in its waters. They would be taken care of by a small army of Navy engineers and logistical personnel.

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

The war effort's logistical needs were supported by Service Squadron 10.

The unit had over 400 vessels, which included repair ships, tanker, 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 fight. They were used as a secret weapon.

It was an important base of operations. The troops could rest and recuperate after a ship was repaired or mended enough to return to a bigger base. There are aircraft carriers moored there.

The invasion of Iwo Jima and the liberation of the Philippines all took place from Ulithi. Preparing for the invasion of Japan's home islands was one of the things it hosted.

USS Mississinewa sinks at Ulithi
USS Mississinewa after being hit by a Japanese Kaiten manned torpedo on November 20, 1944.
US Navy

As of the end of the war, Ulithi hosted as many as 617 vessels. Ulithi was a target because of the large number of ships.

Japanese aircraft, mini-subs, and Kaiten manned torpedoes were used to attack it. Some 63 sailors and officers were killed when the Japanese sank the fleet oiler.

25 men were killed and 106 were wounded when a long-range plane hit the carrier. The invasion of Okinawa took place a month after the repair of Randolph.

Japan sent planes and submarine to attack Ulithi. When Japan surrendered, the subs were on their way back.

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

Increased tensions with China are making another war in the Pacific more likely, but the atoll of Ulithi is still relevant.

Modern guided-missile warships can't be rearmed while at sea, so a forward base would be useful.

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.

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

Repairs of battle- damaged ships are more difficult due to the complexity of modern warships and the US's decision to sell naval repair assets after the Cold War.

The US Navy is having a hard time with repairs. Navy officials said this month that the fleet would be reduced by about 10 ships a year because of the 4,200 days of maintenance delays it faces.

The Navy needs every advantage it can get with China continuing to build ships, expand its missile arsenal, and have more industrial capacity than the US.