A Lieutenant Commander with the Indian Navy drowned in an accident involving submarine INS Shankush, about 60 nautical miles off the coast of Mumbai on Monday.The incident happened when Shankush, the Shishumar class submarine, surfaced and four sailors went up to the hull of the boat to carry out maintenance work, sources said.The sea was very choppy and a strong wave swept one of the sailors away. Commander Firdosh Mogal, executive officer of the ship, was on top of the submarine and tried to save him. But another wave swept the officer away, informed the Ministry of Defence's Chief Public Relations Officer Captain Manohar Nambiar.The Navy, along with the Coast Guards, rescued the sailor, but the officer died after his head hit the hull of the submarine. The rescue team retrieved his body. A case of accidental death has been registered at Yellow Gate police station, sources said.