a version of the sh.iii passed a 40-hour endurance test in june and the aircraft were cleared to return to service in july. in the meantime they had been upgraded with the addition of a new rudder, balanced ailerons and had the cowling cut-away for improved cooling. some sources also claim that the original engines were replaced with the improved sh.iiia engines. another thirty new aircraft with these features were built and all eighty of the improved design entered service in home defense units where their climb rate made them excellent interceptors.