The Junkers Ju-188 evolved from the excellent ju 88, but incorporated vast improvements in speed, ceiling and manoeuvrability. Such characteristics, combined with a heavier defensive armament, were expected to make it capable of competing successfully with the enemy fighters. The prototype flew in 1941 and from its design two versions evolved, the A and E, substantially identical except for the engines. The Air Force specification called for interchangeable power plants: the A version was fitted with liquid-cooled Jumo in-line engines, the E version with air-cooled BMW radials. The 188 differed from the Ju 88 primarily in having high-powered engines, a lengthened and streamlined fuselage, a wider span with tapered wings, a modified tail section, a redesigned and largely windowed cockpit and especially better armament.