By the start of Operation Barbarossa, the German invasion of the Soviet Union in 1941, the 21 panzer divisions had undergone further reorganisation to now consist of one tank regiment (of two or three battalions) and two motorised regiments (of two battalions each). Until the winter of 1941/42, the organic component of these divisions consisted of a motorised[4] artillery regiment (of one heavy and two light battalions) and the following battalions: reconnaissance, motorcycle, anti-tank, pioneer, field replacement, and communications. The number of tanks in the 1941-style divisions was relatively small, compared to their predecessors' composition.