In 1939, Slovakia signed a protection agreement with the German Reich and joined the attack on Poland, where its Avia B-534-equipped fighter squadrons claimed their first kills. In October 1942, having made do with obsolete aircraft, the Slovaks were equipped with Bf 109Es and eventually acquired 43 Messerschmitt fighters. The Slovaks would claim over 21 kills. Although it supported German efforts in Yugoslavia and Greece, Bulgaria did not declare war on Russia. First seeing action in August 1943, Bulgarian fighter pilots used their Bf 109Gs to good effect. From late 1943 through to mid-1944, the Bulgarian pilots attempted to defend the country from American bombers, and Stoyanov and Bochev made ace during this period.