On 4 July 1942, American airmen flew in US-built bombers against a German target for the first time. It was a small operation involving six US crews in Boston medium bombers, but was nonetheless a harbinger of things to come. The first heavy bombardment group of B-17s had crossed the Atlantic in June 1942, another arriving by 1 August, marking the first steps in the massive build-up of B-17s and B...