The longest confirmed shot fired against an enemy naval unit using a 16"/50 caliber gun appears to have occurred during the raid against Imperial Japanese Navy units at Truk Atoll, when Iowa straddled a destroyer at 35,700 yards, while the longest shot every fired by a 16"/50 caliber gun in a non-combat situation is alleged to have occurred during an unauthorized naval gunnery experiment conducted 20 January 1989 off the coast of Vieques, Puerto Rico by Iowas Master Chief Fire Controlman, Stephen Skelley, and Gunnery Officer, Lieutenant Commander Kenneth Michael Costigan, who claimed that one of the 16 inch shells traveled 23 nautical miles .