After the "Primrose" grounded on the North Sentinel Island reef on 2 August 1981, crewmen several days later noticed that some men carrying spears and arrows were building boats on the beach. The captain of "Primrose" radioed for an urgent drop of firearms so his crew could defend themselves. They did not receive any because a large storm stopped other ships from reaching them, but the heavy seas also prevented the islanders from approaching the ship. A week later, the crewmen were rescued by a helicopter under contract to the Indian Oil And Natural Gas Corporation (ONGC).