One of the Iris Vs was converted for use as a testbed for the Napier Culverin flying in this form in June 1937 and continuing flight trials until April 1938 .
The Napier Culverin is a licence - built Junkers Jumo 204 diesel engine .
One of the Iris Vs was converted for use as a testbed for the Napier Culverin , a licence - built Junkers Jumo 204 diesel engine , flying in this form in June 1937 and continuing flight trials until April 1938 .