German Tank
One of the first German tanks VK31 (to preserve the secrecy of the named “Leichttraktor” – “light tractor”) was designed by two firms (Krupp and Rheinmetall).
Two Rheinmetall prototypes on “tractor” chassis were tested in the USSR Kazan firing field in 1930-1932. The tests gave unsatisfactory results, and the tank was not built in the series.