The Luftwaffe was also instrumental in the Second Battle of Kharkov destroying enemy airpower of 615 aircraft whilst destroying hundreds of tanks. The German air-arm had helped the Army achieve another spectacular victory. As Fall Blau began the Luftwaffe wiped out the strong contingent of VVS forces and were instrumental in disrupting supply lines and destroying enemy troop and vehicle concentrations. By 19 November, 2,846 Soviet aircraft were destroyed. In an unwelcome turn of events for the Luftwaffe the Soviets started to operate large numbers of British lend-lease aircraft like the Hawker Hurricane. In the opening month the Luftwaffe lost 251 aircraft but the advance was in full swing and the Germans looked set to take the Kuban food producing region and the Baku oil fields. Due to appalling losses Soviet resistance in the air was radically reduced in August. But even without the threat of enemy air attack the Wehrmacht's supply lines were long and difficult to maintain. The Luftwaffe continued to pound the Soviet Navy's Black Sea Fleet and inflicted heavy losses to Soviet Shipping. From February–August the Germans had sunk 68 freighters, a flotilla leader, three destroyers and three submarines. Despite such successes and air support the advance had slowed to a "snail's pace" in the Kuban region, with its forces spread thin, the Luftwaffe was powerless to prevent Soviet aircraft inflicting considerable losses to the Army. As the Battle of Stalingrad got underway the Luftwaffe was now operating often from poor airfields, which caused accidents and damaged aircraft, which the Luftwaffe could ill afford. As a result of the bombing of Stalingrad, which was largely destroyed, the Luftwaffe created ruins in which the Red Army could defend effectively. The Luftwaffe had, by October 1942 flown over 20,000 individual sorties but its original strength (in the shape of Luftflotte 4 with 1,600 aircraft) had fallen 40% to 950 aircraft. The bomber units had been hardest hit having only 232 out of a force of 480 left. The Luftwaffe still held air superiority but clearly its strength was being eroded. The Russian output of aircraft continued unabated—no matter how many enemy machines were destroyed, more appeared, while its own much smaller losses, particularly among the crews, were becoming serious. The Luftwaffe's Sturzkampfgeschwader made maximum effort during this phase of the war flying 500 sorties per day and causing heavy losses among Soviet forces losing just an average of