ROSTOCK, Germany — The U.S. and NATO allies will launch scaled-back drills in the Baltic Sea this week, as conflicts in other regions draw ships away, though the exercise will still send a message of unity and strength to Russia, a senior German military official said. The annual exercise, held for more than five decades since 1971, brings together some 20 vessels from 15 nations with around 6,000 personnel - roughly half the size of last year’s drills - during a period of heightened tensions