India, March 8 -- The sinking of an Iranian naval warship in the eastern Indian Ocean offers a stark reminder of how quickly the comfortable assumptions of peacetime maritime diplomacy collapse once war begins. The IRIS Dena had reportedly left Visakhapatnam well before hostilities broke out. Yet by the time it was transiting the Indian Ocean, it had become a hunted ship. A US submarine torpedoed it about 40 nautical miles south of Galle, in waters within Sri Lanka's Exclusive Economic Zone (EEZ), but legally open to foreign military operations.

The episode has exacted a heavy human toll. Of a crew strength of 187, 87 are reportedly dead. Officers and sailors who only days earlier had participated in a multinational naval exercise sudden...