The occupation of Ulithi

On 23 September 1944 soldiers of the 323rd Infantry Regiment of the US 81st Infantry Division came ashore on the islets of Ulithi, a vast atoll in the western Carolines. Not a single shot was fired: the Japanese garrison had left the atoll several months earlier. At the same time, a few hundred kilometres to the south-west, the 1st Marine Division was bleeding in the Battle of Peleliu. The contrast was striking: the island captured at the cost of thousands of killed and wounded turned out to be of little importance, while the atoll taken without loss became, within a few weeks, one of the most important bases of the American fleet in the entire war.

War chronologies record that the Americans occupied the great atoll of Ulithi, which later became an important naval base. Both the date and the description are correct. It should only be added that a reconnaissance party landed on one of the islets as early as 21 September, the main force came ashore on 23 September, and the operation was declared complete over the next two days.

An atoll at the end of the world

Ulithi consists of some 40 low coral islets with a total area of only a few square kilometres, strung around the rim of a lagoon more than 30 kilometres long and more than 20 wide. The lagoon, mostly 20–30 metres deep and sheltered by the reef, is one of the largest in the world. The atoll lies roughly 580 kilometres south-west of Guam, about 190 kilometres north-east of the island of Yap and about 1,400 kilometres from the Philippines. At the time it had a few hundred inhabitants, living mainly on the islets of Falalop, Mogmog, Asor and Fassarai.

The Caroline archipelago had belonged to Spain, which sold it to Germany in 1899. In 1914 the Japanese seized the German possessions north of the equator, and after the war they governed them as a League of Nations mandate. On Ulithi they built a radio and weather station, and on Falalop an airstrip; their ships used the lagoon only occasionally. In 1944, after American carriers had already destroyed the great base at Truk atoll in Operation Hailstone and the front was approaching the Carolines, the Japanese withdrew the garrison from Ulithi – according to the islanders’ accounts, several months before the American landing.

A change of plans

The American fleet needed sheltered anchorages ever closer to Japan and the Philippines. After the capture of the Marshall Islands, the lagoons of Majuro and Enewetak served as forward bases, but the front was moving further west. Ulithi had featured from the start in the plans for Operation Stalemate II, whose first phase was the landing on Peleliu and Angaur and whose second was the landing on Yap and Ulithi.

In mid-September the plans changed. Admiral William Halsey proposed abandoning the intermediate objectives and bringing forward the invasion of the Philippines. The Joint Chiefs of Staff moved the landing on Leyte up to 20 October, and the two divisions earmarked for Yap – according to the Marine Corps history of the operation, the 77th and 96th Infantry Divisions – were handed over to General Douglas MacArthur. The attack on heavily defended Yap was dropped, but Ulithi, because of its lagoon, was considered too valuable to let go. According to the same history, Halsey instructed Vice Admiral Theodore Wilkinson to seize the atoll “with the forces at hand”. The only unit available was the 323rd Infantry Regiment, which was being held in reserve off Palau in case of trouble on Peleliu or Angaur. On 16 September it was assigned to take Ulithi. The naval task group was commanded by Rear Admiral William Blandy.

A landing without an enemy

The first detachment – the regiment’s reconnaissance platoon, reinforced by two dozen soldiers – reached the atoll on the morning of 21 September and in the afternoon went ashore unopposed on the islet of Mangejang at the entrance to the lagoon, to cover the minesweepers and the frogmen clearing the passage. On 22 September soldiers who had paddled in rubber boats to the islet of Fassarai brought two islanders back to the ship. From them the Americans learned that there were no longer any Japanese on the atoll.

On the morning of 23 September the main force landed on Falalop, where the airstrip was, and in the afternoon on Asor. No Japanese soldiers were found, only a few graves and two bodies in shallow water. Some of the inhabitants of Falalop had sheltered in a cave from the expected fighting and returned to their village only after much persuasion. Over the following hours the remaining inhabited islets, including Mogmog, were occupied. Equipment and supplies had been unloaded by 25 September; that day the development of the atoll into a base was taken over by Vice Admiral John Hoover’s Forward Area, Central Pacific command. For the duration of the war the islanders were moved to the islet of Fassarai. The operation’s only serious loss was the minesweeper YMS-385, which sank after striking a mine in one of the passages into the lagoon on 1 October.

A floating base

At the beginning of October, ships of Service Squadron 10 under Commodore Worrall Carter, which Admiral Chester Nimitz called his “secret weapon”, began arriving at Ulithi. Within a month the lagoon had become a floating port: at anchor lay repair ships, tenders, oilers, ammunition and provision ships and floating docks (PL) capable of lifting even a battleship. The navy’s construction battalions, the Seabees, enlarged the airfield on Falalop and built pontoon piers, seaplane bases and depots, and on Mogmog a recreation centre where thousands of sailors from the ships in the lagoon could relax at the same time.

As a result the fleet no longer had to return to Hawaii or to distant bases in the Marshall Islands for repairs and supplies. Oilers sailed from Ulithi to meet the carrier task groups and refuelled them at sea, not far from the area of operations. According to American studies, the lagoon could accommodate several hundred ships, and in March 1945, before the invasion of Okinawa, more than 700 vessels lay there at once. For several months around the turn of 1944 and 1945 it was probably the largest and busiest anchorage in the world.

Significance

The occupation of Ulithi completed the chain of American bases from the Marianas to Palau, cutting off the Japanese garrisons on Yap, Truk and elsewhere in the Carolines, which were henceforth left to their own devices. From the lagoon sailed the fleet groups that covered the landing on Leyte in October 1944 and fought the Battle of Leyte Gulf, and in the spring of 1945 the invasion forces bound for Okinawa. The Japanese tried to strike at the base: on 20 November 1944 a kaiten human torpedo sank the oiler USS Mississinewa in the lagoon, and in March 1945 a kamikaze aircraft damaged the carrier USS Randolph lying at anchor there. Neither attempt disrupted the work of the base.

After the capture of the Philippines and Okinawa the fleet moved its forward bases further west, and Ulithi quickly emptied. Because the censors long forbade any mention of the atoll, its name remained almost unknown to the American public. Historians of the Pacific War agree, however, that the bloodless occupation of Ulithi gave the Americans more than the hard fighting for Peleliu: it was this lagoon, not the airfield on Peleliu, that became the rear base for the further offensive towards Japan.