The Messerschmitt Me210 was designed as a 2 seat heavy fighter to replace the Bf110. It had two unique features, the first being a small bomb bay under the forward cockpit that could take up to 2 SC 250 or SC 500 bombs, the second feature was the defensive 13mm machine guns that were housed in remotely controlled barbettes on each side of the rear fuselage. The Me210 was not a success with major stability and handling problems.
The Me 410 was a revised version of the 210 that cured the 210's main problems. It had a lengthened fuselage, modified wings and leading edge slats which cured the handling problems, and the 410 also was fitted with the more powerful DB603 engines. The standard fixed armament was 2 MG151 20mm cannons and 2 MG 17 7.92mm machine guns in the nose, as well as the defensive guns. The bomb bay could also house further weapons in place of bombs, the most common of which would be another 2 MG151's but it could also take a BK5 50mm gun for shooting down bombers. Some also carried an additional 2 MG151's in a belly pack or a pair of Mk108 30mm cannons in the belly pack. It also had wing bomb racks that could take up to 4 SC 50 bombs or Granaten Werfers.
The A-1 model was the light bomber version. The B-1 was the same as the A-1 with more powerful engines and the nose 7.92mm MG's were replaced with 13mm MG's. Both the A-1 and B-1 could carry more guns instead of bombs for use as bomber destroyers. The U4 designation is for the bomb bay mounted BK.5. The BK.5 was a 50mm gun adapted from the 50mm anti tank gun used in the Panzer III tank.