Jean and Scott Adam of Southern California, and Phyllis Mackay and Robert Riggle of Seattle are the four Americans who were killed by Somali pirates off of the Horn of Africa early today, according to reports. Gunfire erupted when the U.S. Navy, which was shadowing the Americans’ yacht after it was hijacked off of the coast of Oman on Friday, moved in to attempt to negotiate the hostages’ release. (The 58-foot yacht appeared to be headed toward land in Somalia — apparently once hostages reach the shore, options for release become extremely limited.) When the Navy ship approached, a grenade was shot and gunfire heard aboard the yacht. In response, a small team of Navy Seals was dispatched on a rescue mission, but they were too late. Two of the Americans were already dead, and the others injured too severely to save. Two pirates were also killed and thirteen taken into custody. The four travelers were on a trip around the world distributing Bibles to remote schools and churches. They are the first American hostages to be killed by Somali pirates since the wave of hijackings began in the early nineties.