The Junkers Ju.88 A-4, was the most important version of all Ju.88 A-series and it entered service in very small numbers in 1939, equipped significant numbers of units during 1940, and was the most important German bomber at the start of Operation Barbarossa in 1941. The A-4 solved the problems that had limited the performance of the A-1, increasing the wingspan, using more powerful engines as 1,400hp Jumo 211F or 211J, fortifying the internal armor (especially around the cockpit), and increasing its rate of fire, carrying five guns and a bomb load of 7,936lbs.