The M-1 night bomber version, equivalent to Do 217 K-1 but with DB603A engines. Carried similar armament and bomb load to K-1. Daimler-Benz DB 601s were also used on some variants to keep the airframes in service (the shortage of powerplants made this difficult). Mostly though, DB603A-1 engines were used on the M-1, its only major difference with the K series. The M-1/Umrüst-Bausätze 1 (abbreviated "/U1") incorporated the M defensive armament and the lattice air brake of the E-2. The MG 81Z and 131 were to be replaced by the MG 151 in the A-stand position. Problems with the air brakes prevented serial conversions.

By November 1943 the M-1/U1 had matured into a night bomber with anti-glare protection in the cabin. The machine was equipped with a MG 131 in the nose, two MG 81Js in the cabin windows and two MG 131s in the B and C stand. Some M-1/U2s fitted with Kehl IV and rear-looking FuG 216 Neptun R radar equipment. 438 M-1 were built by Dornier in Munich and Wismar.

Sources:
Gunston, Bill - The Encyclodepia of the Worlds Combat aircraft, 1976, Chartwell Books, Inc., New York
Brown, Eric, Captain - Wings of the Luftwaffe, 1979, Airlife Publishing Ltd., Shrewsbury
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London
Donald, David - The Complete Encyclopedia Of World Aircraft, 1997, Brown Packaging Books Ltd., London
Wikipedia - Dornier Do 217