From the Avalanche Press website:
Germany founded its first panzer division in 1935, converting the 3rd Cavalry Division to a powerful but unwieldy tank formation. The 1st Panzer Division fought in the French campaign of 1940 with the same organization used in Poland. All of the panzer divisions had variations in their order of battle, and 1st Panzer Division was slightly larger than most of the others. This continued after an Army-wide reorganization in the fall of 1940.
In preparation for the sneak attack on the Soviet Union, the German Army greatly expanded the number of its panzer divisions, making each of them smaller in the process. The greater number of divisions stroked Adolf Hitler's ego, which was important, but it also gave each smaller division a higher ratio of infantry to tanks, which analysis of the Polish and French campaigns had identified as a major weakness of the old-model division.
Ending up in and around Cherbourg at the close of the French campaign, 1st Panzer Division shifted to East Prussia by rail to begin its re-organization. 1st Panzer Division gave up its 2nd Panzer Regiment along with about half of its tanks, sending them to the new 16th Panzer Division then forming from the 16th Infantry Division. In keeping with the tradition of armies everywhere, all of the division's useless Panzerkampfwagen I tankettes were assigned to the departing unit. The two tank battalions remaining kept their PzKw IVE support tanks but received new-model PzKw III medium tanks with the new 50mm gun.
In exchange, the division received a newly-organized battalion of motorized infantry and switched from one regiment of three battalions to two regiments each of two battalions. It added a company of heavy infantry guns for direct support, but the artillery regiment remained steady at two light battalions with 105mm howitzers, one medium battalion with 150mm howitzers, and one anti-tank battalion with 36 towed 37mm anti-tank guns. Unlike most of the other divisions, 1st Panzer kept its motorcycle battalion.
1st Panzer Division provides the complete fighting unit in its own special color scheme: 330 pieces with all the troops and tanks and guns to field the division as it stood in June 1941. It is perfect for use with Eastern Front and Campaigns & Commanders: War in the East. Originally provided as a download, as of March 2015, it is available in printed form to members of the Gold Club.