to risk an attack without air support. In the meantime, Fliegerkorps IV, was forced to use every available aircraft. Although meeting more numerous Soviet air forces, the Luftwaffe achieved air superiority and limited the German ground forces' losses to Soviet aviation, but with some crews flying more than 10 missions per day. By 15 May, Pflugbeil was reinforced and received Kampfgeschwader 27 (Bomber Wing 27, or KG 27), Kampfgeschwader 51 (KG 51), Kampfgeschwader 55 (KG 55) and Kampfgeschwader 76 (KG 76) equipped with Junkers Ju 88 and Heinkel He 111 bombers. Sturzkampfgeschwader 77 (Dive Bomber Wing 77, or StG 77) also arrived to add direct ground support. Pflugbeil now had 10 bomber, six fighter and four Junkers Ju 87 Stuka Gruppen (Groups). Logistical difficulties meant that only 54.5 per cent were operational at any given time. German defence German close air support made its presence felt immediately on 15 May, forcing units such as the Soviet 38th Army onto the defensive. It ranged over the front, operating dangerously close to the changing frontline. Air interdiction and direct ground support damaged Soviet supply lines and rear areas, also inflicting large losses on their armoured formations. General Franz Halder praised the air strikes as being primarily responsible for breaking the Soviet offensive. The Soviet air force could do very little to stop Pflugbeil's 4th Air Corps. It not only attacked the enemy but also carried out vital supply missions. Bombers dropped supplies to encircled German units, which could continue to hold out until a counter-offensive relieved them. The 4th Air Corps anti-aircraft units also used their high-velocity 8.8 cm guns on the Soviet ground forces. Over the course of the 16-day battle the 4th Air Corps played a major role in the German victory, conducting 15,648 sorties (978 per day), dropping 7,700 tonnes of bombs on the Soviet forces and lifting 1,545 tonnes of material to the front. On 14 May, the Germans continued to attack Soviet positions in the north in localised offensives and by then, the Luftwaffe had gained air superiority over the Kharkov sector, forcing Timoshenko to move his own aircraft forward to counter the bolstered Luftflotte 4. The Luftwaffe won air superiority over their numerically superior, but technically inferior opponents. The air battles depleted the Soviet fighter strength, allowing the German strike aircraft the chance to influence the land battle even more. Nonetheless, the Soviet forces pushed on,