Hello Dave and Ian, not wanting to confuse this too much, while the Idflieg designation for the Junkers armoured ground attack aircraft was ‘J.I’, internally at Junkers it was the ‘J4′ being their fourth production aircraft. The only reason I mention this is that Junkers’ first aircraft was also ‘J1’ and is referenced frequently as being the original Dessau Donkey and first all metal monoplane.

Regards
John