The Do 217K-2 was developed as a version of the Do 217K-1 bomber designed to carry the Ruhrstahl SD 1400 X guided bomb, also known as Fritz-X. The key modification was an extended wingspan of nearly 25 meters – necessary to handle the significantly increased combat load, as a single guided bomb weighed 1570 kg. To preserve flight range, an additional 1160-liter fuel tank was installed in the forward bomb bay. Two special racks for the Fritz-X bombs were mounted under the wings between the fuselage and engines. The German company Ruhrstahl A.G. developed the bomb, designed by engineer Max Kramer. It was an armor-piercing glide bomb for attacking armored naval targets, with flight control from the aircraft via radio waves. The carrier bomber had to fly at an altitude of at least 4 km. The Fritz-X carried 360 kg of explosives and could penetrate 130–150 mm of armor—sufficient to destroy even battleships. The most famous use of the Do 217K-2 bomber (crew commander Major Bernhard Jope) and the Fritz-X bomb was the sinking of the Italian battleship Roma on September 9, 1943.