As President Franklin Roosevelt put it in 1943, "Hitler built walls around his ‘Fortress Europe' but he forgot to put a roof on it." The Mighty Eighth would eventually achieve its objectives through relentless bombing of German airplane factories, submarine pens, oil refineries, railway yards, ball bearing production facilities and other industrial targets deemed central to the Nazi war effort. In the beginning it would do it alone, without fighter escorts, another untested approach. But against the dug-in Nazis there seemed no other way.