 Her first success came on 29 May when she sank the unescorted British 1,597 ton cargo ship "Allister", en route from Kingston, Jamaica, to Tampa, Florida, with a cargo of 500 tons of bananas.The ship was torpedoed south of Grand Cayman Island, losing 15 of her crew of 23.On 8 June "U-504" struck twice, east of the Yucatán Peninsula.