As a military aircraft, it took longer to gain favor, because military load requirements and underpowered engines kept its cruising speed down to less than 170 mph. However, in early 1936, the plane was given 1,000 hp Daimler Benz DB 600A engines which improved performance dramatically enough to bring in substantial orders. The first two mass-production versions, He 111 E and He 111 F experienced great success during the Spanish Civil War, where they served with the Condor Legion as fast bombers, able to outrun many of the fighters sent against them.