Immediately after an explosion that caused the 1,200-ton corvette Cheonan to sink in waters near the de-facto maritime border with North Korea on March 26, the Captain sent out a message to the Second Navy Fleet Command, saying, "We are being attacked by the enemy." A military source on Thursday said Captain Choi Won-il sent the message using his mobile phone, according to analysis of communications records. Choi sent the report after confirming that the stern had broken off following the explosion around 9:25 p.m. It is not clear how much information he had at the time.