 The serial numbers matched those of mines seized along with the Iran Ajr the previous September.By the time "Roberts" was towed to Dubai on 15 April, battered but saved with no loss of life, U.S. planning for the retaliatory operation had already begun in Washington and in the Middle East.The battle, the largest for American surface forces since World War II, sank two Iranian warships and as many as six armed speedboats.