Location
Ulithi Atoll surrounds Ulithi Lagoon (Urushi Lagoon) in the western Pacific Ocean. Also known as Urushi Atoll. Prewar and during the Pacific War part of the western Caroline Islands. American code name "Mackenzie". Today located in in Yap State in the Federated States of Micronesia. To the west-southwest 106 miles away is Yap. To the north 1,300 miles is Tokyo and 850 miles to the west is the Philippines. To the northeast 360 miles is Guam.

The Ulithi Atoll have a total land area of 1.75 square miles and include: Pugeluc Island, Feitabul Island, Lossau Island, Fassarai Island (Aggravate), Mugai Channel, Mangejang Island (Amazement), Falalop Island (Ameliorate), Asor Island (Identical), Sorlen Island (Keenset), Mogmog Island (Litharge), Potangeras Island (Acetylene).

Prewar
Several hundred Micronesian people lived on several of the larger island in Ulithi Atoll including Sorlen, Falalop, Asor, and Mogmog.

Wartime History
During the Pacific War, Occupied by the Japanese and used to a limited degree until abandoned by September 1944. During 1944, U.S. Navy (USN) carrier aircraft conducted combat missions and photo intelligence against Ulithi.

American missions against Ulithi
March 30, 1944–September 20, 1944

On September 20, 1944 occupied by U.S. Army 81st Infantry Division without opposition finding only three Japanese and 400 native people living on Sorlen, Falalop, Asor, and Mogmog that were consolidated and moved onto Fassarai Island.

Afterwards, Ulithi was developed into a major U.S. Naval base and Ulithi Lagoon (Ulithi Anchorage) as an anchorage for the 3rd Fleet and 5th Fleet for the remainder of the Pacific War. From this location, U.S. Navy (USN) warships and carriers sortied for the Battle of Leyte Gulf and the invasion of Okinawa and would have departed Ulithi for Operation Olympic the planned invasion of Japan.

On October 1, 1944 the 18th Special Battalion arrived at Ulithi with 17 officers and 514 enlisted men quartered on a barracks barge. The battalion was to stevedore for the fleet and was essential as all supplies, fuel, ammunition, and spare parts were stored afloat and handled an average of 20,000 tons of cargo each month until May 25, 1945, when ordered to Leyte Gulf. On October 10, 1944, a detachment of the 6th Special Battalion arrived at Ulithi to operate as a ship-to-shore stevedoring unit and handled an average of 12,000 tons of cargo until June 1945 when it returned to Pearl Harbor.

Loran
A small Coast Guard station was built for navigation, closed after the war.

Ulithi Lagoon (Urushi Lagoon)
Located at the center of Ulithi Atoll world's fourth largest lagoon with an area of 209 square miles.

Falalop Island
Located at the eastern edge of the Ulithi Atoll including Falalop Airfield (Ulithi Airfield)

Mogmog Island
Located on the northern edge of Ulithi Atoll developed into a fleet recreation area.

Sorlen Island
Located on the northern edge of Ulithi Atoll developed into a fleet recreation area.

Lossau Island (Lossad)
Located at the southeast edge of Ulithi Atoll.

References
Building the Navy's Bases Online Ulithi, in the western Carolines
History of the U.S. Marine Corps Operations in World War II - Chapter 5 Angaur and Ulithi pages 180-184

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Last Updated
October 23, 2019