Mobjack (AGP-7) was laid down as a seaplane tender, AVP-27, by Lake Washington Shipyard, Houghton, Wash., 5 February 1942; launched 2 August 1942; sponsored by Mrs. E. R. Peck; reclassified as AGP-7, 11 March 1943; and commissioned 17 October 1943, Comdr. D. B. Coleman in command.

Following shakedown off southern California, Mobjack departed San Diego for the southwest Pacific 14 December 1943. Steaming via New Caledonia and the New Hebrides, she arrived at Rendova, British Solomon Islands, 14 January 1944 to begin duty with MTBRons, SOPAC. She trained and supplied PT's in the New Georgia area until 6 March 1944, when she steamed to Treasure Island and thence to the MTB base, Emirau, arriving on the 23d. In mid-May fihe returned to Treasure Island where she overhauled PT's and repaired and tended the PGM and LCI gunboats of TG 30.3 into July.

Employed briefly in transporting spares and other materiel, she departed for British New Guinea on the 23d, arriving at Dreger Harbor on the 27th to begin service under ComMTBRons, 7th Fleet. During the greater part of August she operated at Altape Harbor, tending MTBRBon 33 and providing assistance in salvage work. On the 28th, she got underway for Mios Woendi, Netherlands New Guinea, in company with MTBRBon 33. Arriving there on the 31st, she was engaged in fueling, provisioning and making final repairs to the boats of the squadron preparatory to sailing for Morotai as a unit of TG 70.1.

Arriving at Morotai 16 September, D-plus-1 day, she commenced tending the boats of her squadron and PBYs assigned to air/sea rescue of pilots downed en route to and from raids on Truk. For the first 3 days she went about her duties unscathed in spite of enemy air resistance. At sunrise on the 19th, however, a smoking Japanese flghter emerged from a heavy overcast and dove for Mobjack. Unable to crash the ship, the pilot dropped two bombs which exploded close alongside, holing the deck and wounding one of her crew. Making temporary repairs, she remained at Morotai, tending PT boats of TU 70.1.2 and PBYs now ranging over the Netherland Fast Indies on relief and intelligence reconnaissance missions, until February 1945.

During February and March she transported materiel, spares, and advanced base personnel as she accompanied MTB squadrons to forward areas. At Mios Woendi, 1 April, she took on base force personnel of MTBRons 9 and 10 and the next day got underway for Samar, Philippine Islands. Arriving on the 11th, she disembarked her passengers and steamed on to Palawan where she relieved Willoughby as the repair unit for MTBRons 20 and 23. She moved on to Mangarin Bay, Mindoro, in mid-May to overhaul and repair MTBs for use in the Philippines and in the upcoming Borneo operations.

On 8 June she steamed to Samar to stage for the landings at Balikpapan. Departing an the 21st, she sailed, with MTBRons 10 and 27 to Basilan Island, thence, on the 26th, further down the Sulu Archipelago and Into Makassar Strait. The following day she joined the minesweepers, at work since 1 June, and the ships of the bombardment group, which had been pounding the Japanese held oil center since the 17th, in preparing the way for the Australian assault force. For four days Mobjack fueled and subsisted the MTBs assigned to night patrol off the coast to prevent the Japanese from remining, restoring obstacles blown by underwater demolition teanis, or disturbing channel markers planted by the minesweepers. On 1 July, these extensive preparations and precautions proved to have been well executed as wave after wave of 7th Division, 1 Austalian Corps personnel went ashore without a casualty.

Mobjack, harassed by Japanese night air attacks until RAAF night fighters proved too accurate, remained outside the harbor for the next 9 days. On the 11th she stood into the harbor, where, on 15 August, she received a dispatch directing the cessation of all offensive action against the Japanese.

On 12 September, Mobjack returned to the Philippines and for the next 2 months engaged in decommissioning MTBs under ComMTBRons, Philippine Sea frontier. On 10 November she sailed eastward, arriving at San Francisco on the 29th. The following month stripping was begun and on 21 August 1946 Mobjack decommissioned. Transferred, the same day, to the custody of the Department of Commerce, she later joined the U.S. Coast and Geodetic Survey as the survey ship Pioneer. Pionner was sold for scrap 4 May 1966 to National Metal and Steel Corp., Terminal Island, Calif.

Mobjack received three battle stars for World War II service.