Over a ten-day period Wanklyn joined the ranks of submarine aces. Simpson received a report from naval intelligence that two enemy cruisers and destroyers were leaving port in Sicily to rendezvous with a convoy south of Kerkennah Islands. Wanklyn was ordered to remain off the island of Lampedusa, midway between Malta and Tunisia. Nothing was seen, so Wanklyn sailed to the Tunisian coast and selected an area well known for its convoy traffic. On 25 April Wanklyn spotted a merchant ship and its armed trawler escort but managed to close to 700 yards undetected before firing two torpedoes. The ship was hit and sank. It was later identified as the small merchant vessel "Antonietta Lauro", which was loaded with nitrates bound for Italy. She sank slowly, and went under after six hours.