Panzer IV ausf F1 production started at Krupp in April 1941 with 395 built through March 1942. Vomag built 64 and the Nibelungenwerke built 13. Some 280 ausf E had been built by the time the ausf F1 began entering service in the spring of 1941. By July 1, 1941, the total number of Panzer IV of all types on hand was 531 units.