USS Mobjack (AVP-27/AGP-7) was a motor torpedo boat tender in commission in the United States Navy from 1943 to 1946. She saw service in the Pacific theater during the latter portion of World War II.
After the conclusion of her Navy career, the ship served in the United States Coast and Geodetic Survey from 1946 to 1966 as the survey ship USC&GS Pioneer (OSS 31), the third Coast and Geodetic Survey ship of the name. Pioneer operated in the Pacific Ocean during her career, making an important discovery of magnetic striping on the ocean floor that made a major contribution to the development of the theory of plate tectonics. She also took part in the International Indian Ocean Expedition, becoming the first ship in the history of the U.S. Coast and Geodetic Survey to visit the Indian Ocean.
Construction and commissioning
Mobjack was laid down as a seaplane tender, AVP‑27, by Lake Washington Shipyard, Houghton Washington, on 25 February 1942 and launched on 2 August 1942, sponsored by Mrs. H. R. Peck. She was reclassified as a motor torpedo boat tender and redesignated AGP‑7 on 11 March 1943 and commissioned on 17 October 1943.
United States Navy service
World War II
Following shakedown off Southern California, Mobjack departed San Diego, California, for the Southwest Pacific on 14 December 1943. Steaming via New Caledonia and the New Hebrides, she arrived at Rendova, British Solomon Islands, on 14 January 1944 to begin duty with Motor Torpedo Boat Squadrons, South Pacific (SOPAC). She trained and supplied patrol torpedo boats (PT boats) in the New Georgia area until 6 March 1944, when she steamed to the Treasury Islands and thence to the motor torpedo boat base, Emirau, arriving on 23 March 1944. In mid‑May 1944 she returned to the Treasury Islands, where she overhauled PT boats and repaired and tended the motor gunboats (PGMs) and landing craft infantry gunboats (LCI(G)s) of Task Group 30.3 into July 1944.
Employed briefly in transporting spares and other materiel, she departed for British New Guinea on 23 July 1944, arriving at Dreger Harbor on 27 July 1944 to begin service under Commander, Motor Torpedo Boat Squadrons, 7th Fleet. During the greater part of August 1944 she operated at Aitape Harbor, tending Motor Torpedo Boat Squadron (MTBRBon) 33 and providing assistance in salvage work. On 28 August 1944, she got underway for Mios Woendi, Netherlands New Guinea, in company with MTBRBon 33. Arriving there on 31 August 1944, she was engaged in fueling, provisioning and making final repairs to the PT boats of the squadron preparatory to sailing for Morotai as a unit of Task Group 70.1.
Morotai
Arriving at Morotai on 16 September 1944, the day after the American landings there, she commenced tending the boats of her squadron and Consolidated PBY Catalina flying boats assigned to air-sea rescue of pilots downed en route to and from raids on Truk. For the first three days she went about her duties unscathed in spite of Japanese air resistance.
At sunrise on 19 September 1944, however, a smoking Japanese fighter emerged from a heavy overcast and dove for Mobjack. Unable to crash into 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 Task Unit 70.1.2 and PBYs now ranging over the Netherlands East Indies on relief and intelligence and reconnaissance missions, until February 1945.
The Philippines
During February and March 1945, Mobjack transported materiel, spares, and advanced base personnel as she accompanied motor torpedo boat squadrons to forward areas. At Mios Woendi on 1 April 1945, she took on base force personnel of MTBRons 9 and 10 and on 2 April 1945 got underway for Samar in the Philippine Islands. Arriving on 11 April 1945, she disembarked her passengers and steamed on to Palawan, where she relieved motor torpedo boat tender USS Willoughby (AGP-9) as the repair unit for MTBRons 20 and 23. She moved on to Mangarin Bay, Mindoro, in mid‑May 1945 to overhaul and repair motor torpedo boats for use in the Philippines and in the upcoming Borneo operations.