The naval base at Ulithi was established to provide a fleet anchorage and an air base to support half of a night fighter squadron, a light inshore patrol squadron, pool for a maximum of 150 carrier replacement aircraft, a utility squadron, and staging facilities for transport aircraft. The basic plan also called for maintaining shore facilities to support the garrison and the fleet.

    This atoll, 93 miles northeast of Yap, 370 miles southwest of Guam, and 370 miles northeast of Peleliu, consists of four elements: the main atoll, in the west; the island of Falalop off the northeast point; a small detached reek with several islets, lying east of the main atoll; and Zohhoiiyonu Bank, an incomplete atoll, to the extreme east.
 All the islets of the group are of typical atoll structure, with low level land, wooded in spots and swamp areas, generally covered with thick vegetation. The rainfall is heavy and the climate tropical. Mogmog Island, in the nort, is the principal islet; others which were most used by our forces are Falalop, Asor, Potangeras, and Sorlen.

    Ulithi Atoll was occupied on September 20, 1944, with no ground opposition by Japanese forces. There were numerous air raids in the early days of the operation, but no damage to Seabees or equipment resulted.

    The 18th Special Battalion arrived on October 1, 1944. This unit, consisting of 17 officers and 514 men, was quartered on a barracks barge. The battalion was to stevedore for the fleet rather than to handle straight shore-to-shore stevedoring operations. This type of work was then highly essential at Ulithi, where all supplies, fuel, ammunition, and spare parts were stored afloat. The 18th Special worked at this task until May 25, 1945, when it was detached and ordered to Leyte Gulf. During that period, the battalion handled an average of 20,000 tons of cargo monthly.

    On October 10, 1944, a detachment of the 6th Special Battalion arried at Ulithi to operate as a ship-to-shore stevedoring unit. During ist service there, the 6th handled a monthly average of 12,000 tons of cargo. This battalion was detached in June 1945 and returned to Pearl Harbor, where it was inactivated.

    The 51st Battalion disembarked on October 8, 1944, with 797 enlisted men and 28 officers, and was assigned the task of widening, lengthening, and improving the Japanese airfield on Falalop Island. A 3,500-by-150-foot runway was completed in 27 days. The east end of the strip extended approximately 20 feet past the natural shoreline of the island, log cribs being used as foundation for this addition to the island. The first plane landed on the strip 15 days after work was begun. Six taxiways were constructed; one, 4,000 by 100 feet; and one, 3,250 by 700 feet; and four, 500 by 100 feet. Also installed were hardstands, lighting, a traffic-control tower, operations buildings, aviation-gasoline ready tanks, and a tank farm; all work was completed by December 1, 1944.

    The first section of the 88th Battalion, consisting of Companies C and D and half of the headquarters company, landed at Ulithi on October 10, 1944. Ist assignment included construction of the shore facilities necessary to use the atoll as a fleet recreation center; improvement of living conditions on all island; and the providing of airstrips for light plane operations. Work was also begun immediately on a camp site.

    A seaplane ramp was constructed at one end of the main airfield on Falalop Island. This ramp, which extended from extreme low-water mark to the hardstand, was 50 by 95 feet, surfaced with pierced plank, and protected along the outer edges by a concrete slab. Work was begun on November 4, 1944, and completed on December 5, five days ahead of schedule.

    A number of pontoon piers of a new and special design were built at Ulithi. These piers, each consisting of the 4-by-12-pontoon sections, filled with sand and gravel, were sunk and anchored in place by guy ropes to deadmen on shore and  by iron rods, driven into the coral, with connecting tie pieces running across the tops of the pontoons. Despite extremely heavy weather on several occasions he pontoon piers stood up remarkably well, giving extensive service, with few repairs necessary. Piers of this type were also installed by the 51st Battalion to be used as aviation-gasoline mooring piers near the main airfield.

    One of the major construction jobs on Ulithi was that of a fleet recreation area on Mogmog Island. The selected area was cleared, and a swamp area filled with coral, to eliminate mosquitoes and insects. Construction of the recreational facilities began on October 15. Numerous facilities for sports, a band stand, and beverage storage were provided. When completed in January 19945, the center could accommodate 8,000 men and 1,000 officers daily. A 1,200-seat theatre, including a 25-by-40-foot stage with a quonset hut roof, completed in 20 days was ready for use on December 20, 1944. At the same time, a 500-seat chapel was built. A similar theatre, seating 1600, was constructed on Sorlen Island in 19 days.

    The construction of facilities for a standard landing-craft unit on Sorlen Island was another major project. This development involved grading the entire island and covering it with quonset huts for storage, shops, mess halls, offices, and living quarters, and building roads, supply dumps, and necessary facilities to supply water and electricity to all parts of the island. Eleven distillation units, drawing water from the sea, and nine 5,000-gallon storage tanks were set up to provide drinking water.
The Sorlen Island hospital, constructed between November 24, 1944, and January 17, 1945, included quonset huts and supplementary facilities to house and operate a 100-bed unit.

    Other construction included the erection of 42 quonset huts for use as a receiving station, and a 1600-man mess hall,<complete with galley, warehouses and refrigeration units. Three strips for light place operations between islands of the atoll were built between December 12, 1944, and January 27, 1945. Additional facilities included the atoll commander’s headquarters, a dispensay, an administration building, a shop and Marine aviation camp.

    All construction was performed by the 88th Battalion between October 10, 1944, and February 7, 1945, at which time the battalion left for Samar.

    On November 8, 1944, CBMU 603 arrived, and in addition to general maintenance of the airstrip and taxiways, constructed a sewage-disposal system for the Marines and for the Seabees galleys. Construction of a 3,000-man galley, a refrigeration storage building, a butcher shop, an issue room, a bakery an officers’ mess, and shops for a landing craft unit was another important task. Other construction included enlarging and improving a finger pier and the removal of 10,000 cubic yards of coral to improve beaching facilities for landing craft. With the departure of the other battalions, CBMU 603 took over all duties of construction, maintenance, and stevedoring.

    On V-J Day, this base was still operating at capacity, with CBMU 603 still attached.