During the course of the war, German forces added command tanks, specialised to the task of co-ordinating tank formations. This idea caught on with other nations. Development of British doctrine added howitzer-armed close support tanks, similar to the older torpedo tank role. These soon became critical to launching smoke, and post-war smoke dischargers became common on tanks. Both command and close support tanks were typically based on the type of tank they were supporting, so may not be considered a completely separate classification.