A significant search operation was underway Thursday in Lithuania for four U.S. soldiers who went missing two days ago during a military training exercise, with both American and Lithuanian forces scrambling to navigate the treacherous landscape. The troops, assigned to the 1st Brigade, 3rd Infantry Division, out of Fort Stewart , Georgia, were last seen aboard an M88 recovery vehicle -- a heavily armored tow truck used to retrieve disabled tanks -- before it was found submerged in deep mud and