President Donald Trump's decision to impose tariffs on European steel and aluminum comes at a particularly delicate time for major U.S. defense contractors Boeing (NYSE: BA), Lockheed Martin (NYSE: LMT), and Raytheon (NYSE: RTN), with each company vying for at least one of several multibillion-dollar procurement deals in Germany.Germany is seeking replacement jet fighters and heavy-lift helicopters, and an update to its missile defense systems.