On 28 July, while in thick fog north of Marettimo, Wanklyn's spotters saw two cruisers supported by destroyers. The escorts were zig-zagging on either side while the cruiser maintained a steady course. It was identified as the "Giuseppe Garibaldi", travelling at high speed—the asdic gave a reading of 230 revs indicating 28 knots. Wanklyn had to think quickly if he was not to miss his chance. At 4,000 yards he fired a spread of four 35-knot Mark IV torpedoes at 12-second intervals. The submarine dived and the crew clearly heard two explosions. The "Garibaldi" stopped as her escorts created a smoke screen and dropped depth charges for 45 minutes. The officers of "Upholder" counted 38. The presence of the escorts and smoke denied the British the chance to assess the results of the attack. "Upholder" returned to Malta and learned that the operation had been a success.