B-1s started rolling off the lines in December 1941, but they were delivered at a trickle. In preparation for the new plane, I./
SchlG 1 had been formed up in January with
Bf 109 E/Bs (fighter-bomber version of Bf 109 E) and
Hs 123s, and they were delivered B-0s and every B-1 that was completed. Still, it wasn't until April that 12 B-1s were delivered and the 4th
staffel (squadron) became ready for action. They moved to the
Eastern Front (to the
Crimea) in the middle of May 1942, and in June they received a new weapon, the 30 mm (1.2 in)
MK 101 cannon with armor-piercing ammunition in a centerline
pod.