Richthofen employed these learned tactics and operational methods during the Battle of Bilbao. The motorised logistics also helped during the rapid redeployment to the south, after the surprise Republican offensive at Brunete in July 1937. The air support was vital in defeating the offensive, which was supported by modern aircraft sent to the Republicans from the Soviet Union. German types like the Messerschmitt Bf 109 fighter, which replaced the Heinkel He 51, the Do 17 and He 111 helped win and hold air superiority and interdict the battlefield. The Republicans had spent most of their gold reserves on buying Soviet equipment. With most of that equipment used up, the Condor Legion and Nationalists gained the technological edge.