NORFOLK, Va. — The attack submarine San Juan lost communications with the outside world for several hours late Tuesday night and early Wednesday, prompting a search effort for what the Navy thought was a downed submarine, according to the Naval Submarine Force Command in Norfolk.One of the scariest scenarios for a submariner is having some sort of casualty that leaves your boat on the bottom, incommunicado.  There are rescue craft available, but somebody needs to (a) realize you're missing and (b) figure out where you are before the rescue effort can get started. That can take an awfully long time. Kudos to the Enterprise strike group for jumping on the ball smartly.
At the time of the incident, the Los Angeles-class submarine, based in Groton, Conn., was operating with the Enterprise Carrier Strike Group off the southeastern coast of the United States.
Because the Navy maintained communications with two other subs in the area and observers spotted a red signal flare, commanders believed the San Juan had gone down. They began search-and-rescue missions, alerted the International Submarine Escape and Rescue Liaison Office and notified crew members' families about the possibility of a lost submarine, officials said.
OTOH, the fact that the statement about "lost communications" makes me curious. Was there a scheduled check-in that San Juan's crew missed? Were they supposed to be guarding a radio channel via their floating-wire antenna? I suspect there won't be any public announcement, unless it turns out that the San Juan's crew screwed the pooch somehow and the Navy relieves the skipper for cause.
 Of course, if the bottom is below the boat's crush depth, rescue is pretty much not an option. In that case, though, the crew will be dead almost instantaneously, so they won't have any agonizing wait for rescue...