Case joined in fleet problems in the Hawaiian area, and in 1938, served as school ship at San Diego. From this, her home port, she carried midshipmen on an Alaskan cruise in summer 1939, and in April 1940 returned to Pearl Harbor to take part in a fleet problem, which found her sailing to Midway, Johnston and Palmyra Islands. Between February and April 1941, she cruised to Samoa, Tahiti and Auckland, N.Z.
Case was in a nest of destroyers at Pearl Harbor Navy Yard on 7 December 1941. The nest opened fire on the attacking Japanese, and splashed several enemy planes in the first action of World War II. From 7 December until 23 May 1942, Case escorted convoys passing between the west coast and Pearl Harbor.
From 31 May to 7 August 1942, Case defied the vicious weather of Alaskan waters, as she patrolled and carried out the usual varied destroyer assignments off Kodiak. On 7 August, she unleashed her guns in the preinvasion bombardment of Kiska, and on an enemy tanker with undetermined results. Case continued on patrol off Adak until mid-October, when she escorted shipping to Pearl Harbor, then proceeded to the States for overhaul.
Returning to Pearl Harbor 21 November 1942, Case cleared to escort a convoy to the Fiji Islands, arriving 20 December. From Fiji, she sailed to Guadalcanal to screen a convoy during its unloading period, and on 1 January 1943, arrived at Espiritu Santo, her base for escort, patrol, and training duty through 23 September After overhaul at San Francisco, Case returned to Pearl Harbor in December.
For the next eight months, Case was almost constantly at sea, screening groups of the Third and Fifth Fleets in their air strikes which paved the way for the advance westward across the Pacific. From mid-January through mid-March 1944, these strikes were hurled at Japanese bases in the Marshalls, supporting the invasion of these islands. Palau and the western Carolines were the targets 30 March–1 April, and Case next sailed from Majuro for the late-April air raids on Hollandia, Truk, Satawan and Ponape. A month of local screening and escort duty at Majuro preceded Case’s assignment to TG 58.4 for the strikes on Japanese airfields in the Bonins, designed to neutralize these bases during the invasion of the Marianas. With this group, she screened carriers in the historic Battle of the Philippine Sea on 19 and 20 June. In this engagement, nicknamed the “Marianas Turkey Shoot,” the back of Japanese naval aviation was broken, which had a decisive influence on the remainder of the war.
After a repair period at Eniwetok, Case resumed operation with TG 58.4, screening for air strikes preparing for the landings on Guam late in July 1944, and the attacks on the Bonins on 4 and 5 August. Through mid-September, Case served on inter-island escort duty in the Marianas. In September, she rendezvoused with two submarines carrying allied prisoners of war—many of them wounded—rescued after the sinking of a Japanese transport. Since rough seas prevented the submarines from transferring the wounded to Case, the destroyer put medical officers on board the submarines
Case participated in the bombardment of Marcus Island on 9 October 1944 and then joined TG 38.1 for strikes on Luzon in conjunction with the invasion of Leyte from 18 to 23 October She returned to Ulithi 29 October, putting to sea again 8 November for the bombardment of Iwo Jima on the night of 11–12 November
Resuming escort duty from Ulithi, Case was screening cruisers bound for Saipan on 20 November, where she rammed and sank a Japanese midget submarine the entrance to Mugai Channel. Immediately, she put back to Ulithi for an inspection of damage incurred in the encounter, but was back in action just two days later, bound for off shore patrol at Saipan until December.
Case joined in a smashing bombardment of Iwo Jima once more on 24 December, during which she and Roe were dispatched to attack a fleeing Japanese transport. A two-hour chase at full speed followed, both destroyers firing as the range closed. At 1559, the effect of accurate gunfire told as the transport sank, her survivors refusing any assistance from the American destroyers. After repairs at Saipan, she returned to Iwo Jima 24 and 25 January 1945 for antisubmarine patrol during the opening phases of operations ashore. Escort and patrol duty from Saipan occupied her until 19 March, when she began an extended period of antisubmarine patrol, air-sea rescue and radar picket duty between Saipan and Iwo Jima until the close of the war. A fitting climax to Case’s fine war record came on 2 September 1945, when she sailed to Chichi Jima to accept and supervise the surrender of the Bonins Islands. On 19 September, she took departure from Iwo Jima for Norfolk, Va., arriving. 1 November. Here she was decommissioned 13 December 1945, and sold 31 December 1947.
Case received seven battle stars for World War II service.