Ideally, the tank battalions of a panzer division were each to have three medium companies of Panzer IIIs and one heavy company of Panzer IVs.[23] The Germans began to convert their tank battalions to a majority of Mark III and IV medium tanks soon after the 1940 French campaign, thereby stealing a march on the Soviets and British, who still possessed obsolete equipment. Panzer III was the first of German Panzers to be equipped with intercom system for in-tank communications. Later on all of Panzers were equipped with this device which, proved to be very effective during combat.