D.XXI, featured a cheap but maneuverable design with fabric-covered fuselage and fixed landing-gear. On paper, the Finnish air assets should have been no match for the attacking Soviet Red Air Force. However, the Finnish Air Force had already adopted the finger-four formation in the mid-1930s, which proved a much more effective formation than the Vic formation that many other militaries continued to use in 1939. To prevent their aircraft from being destroyed on the ground, the Finns distributed their aircraft to many different airfields and hid them in the nearby forests. The Finns constructed many decoys and built shrapnel-protection walls for the aircraft. Soviet air-raids on Finnish airfields usually caused little or no damage as a result, and often resulted in interception of the attackers by the Finns as the Soviet bombers flew homeward. As the war progressed, the Finns tried desperately to purchase aircraft wherever they could. This policy resulted in a very diverse aircraft inventory, which caused some major logistical problems until the inventory became more standardized. The Finnish Air Force included numerous American, British, Czechoslovakian, Dutch, French, German, Italian, Soviet, and Swedish designs. Other countries, like South Africa and Denmark, sent aircraft to assist in the Finnish war effort. Many of these purchases and gifts did not arrive until the end of the hostilities, but would see action later during the Continuation and Lapland wars. To make up for its weaknesses (few and obsolete fighters) the FAF mainly focused on attacking enemy bombers from directions that were disadvantageous to the enemy. Soviet fighters were usually superior in firepower, speed and agility, and Finnish pilots avoided them unless the enemy was in a disadvantageous position. As a result of these tactics, the Finnish Air Force managed to shoot down 218 Soviet aircraft during the Winter War while losing only 47 to enemy fire. Finnish anti-aircraft guns also had 314 confirmed downed enemy planes. 30 Soviet planes were captured – these were "kills" that landed more or less intact within Finland and were quickly repaired. Continuation War (1941–1944) The Finnish Air Force found itself better prepared when the Continuation War against the Soviet Union started in 1941. It had been considerably strengthened and consisted of some 550 aircraft, though many were considered second-rate and thus "exportable" by their countries of origin. Finland purchased a large number of aircraft during the Winter War, but few of those had reached service