Second war patrol, January – March 1944 Following a refit Aspro departed Midway on 15 January and proceeded to Pearl Harbor to undergo brief training before heading back to Midway on 3 February en route to her second patrol. This assignment took her to an area north of Truk, as part of Operation Hailstone. On 15 February at 11:21, she spotted a large Japanese submarine, which was later identified as . After a long surface pursuit, Aspro drew within range of I-43, and at 22:23 fired four torpedoes. Her crew saw and heard an explosion, followed shortly by another. They then saw her target's bow rise as the victim sank by her stern at . This was Aspros first confirmed sinking. On 17 February, she underwent a depth charge attack, but suffered no damage. Aspro torpedoed a freighter on 4 March, and the subsequent explosion shook the submarine violently. However, the Japanese vessel was merely damaged, not sunk. The rest of this patrol passed uneventfully, and Aspro retired to Pearl Harbor on 28 March after 54 days at sea. Third war patrol, April – June 1944 Aspro carried out her third patrol near the Palau Islands. After refitting she got underway on 22 April and headed west. Following a brief stop at Midway for supplies four days later, she continued on to waters around the Palau Islands. On 14 May, the submarine encountered a convoy of two freighters protected by three escorts. At 05:54, she fired a spread of torpedoes at one freighter and, one and one-half hours later, saw the damaged ship lying dead in the water and sinking by the stern. At the end of two hours of intermittent observation, this ship later disappeared from sight. The next day, Aspro attacked one of the escorts of the same convoy and heard one explosion. The submarine's crew watched from the bridge as the target sank. Aspro remained on patrol for another month before reaching Fremantle, Western Australia, on 16 June. There, she was officially credited with sinking one ship and assisting in destroying another for a total loss of 8,650 tons of Japanese shipping. {15 May 1944 the Sinking ship "Jokuja Maru" 6,440 tons was sunk at 10.10N 131.25E} Fourth war patrol, July – August 1944 The submarine spent two weeks undergoing a refit before beginning her fourth patrol on 9 July. After pausing at Darwin, Northern Territory on