The last radio contact was an urgent appeal for help. Night was falling, a rainstorm threatening, and four U.S. Navy SEAL commandos were surrounded by about a dozen militants in rugged, wooded mountains. They needed reinforcements. That hurried call set in motion a chain of events that would lead to the U.S. military's deadliest blow in Afghanistan, and the greatest loss of life ever for the elite force of SEALs. Nine days after the ambush and subsequent downing of a U.S. special forces helicopter with 16 troops aboard, U.S military officials in Kabul and Washington are starting to draw...