The Pyro was moored at West Loch in Pearl Harbor when the Japanese attacked on 7 December 1941. Assigned to Commander, Base Force, Training Squadron 8, she suffered no serious damage and within four days was en route for San Francisco, where she shuttled ammunition from the West Coast to Hawaii until the end of September 1942.
The following month, the Pyro carried a load of mines from San Francisco to Alaska, to be used in the defense of the base at Adak. After returning unharmed to San Francisco, she sailed on 8 December for Espiritu Santo, New Hebrides Islands, where she arrived on 2 January 1943. She operated as the primary ammunition ship there until her departure for San Francisco on 2 August.
The Pyro departed the West Coast for Brisbane, Australia, on 11 November 1943. From 7 December 1943 until 8 April 1944, she transported ammunition from Australia, New Caledonia, and the New Hebrides to Milne Bay, New Guinea. From April through July 1944, she replenished warships engaged in the Admiralty Islands and Hollandia campaigns.
After six weeks of repairs in Sydney, Australia, the Pyro returned to the new base of operations at Hollandia on 9 September 1944. She steamed for Leyte Gulf on 19 December and remained in the area, replenishing combatants until early August 1945, when she sailed for the Admiralty Islands.
As soon as her repair and overhaul at the Admiralties were complete, she sailed for Seattle, arriving on 21 November 1945. The Pyro remained in service until 12 June 1946, when she was decommissioned. She was sold for scrap in March 1950.