Most of the first airmen were armed with revolvers or machine guns and sometimes they had bombs, which they dropped over the sides of their cockpits. Gradually planes developed into fighting machines. For example, Antony Fokker, a Dutch engineer working for the Germans, invented a mechanism that meant airmen could fire through the blades as the propellers went round. Planes on both sides fired on men in the trenches. Dog fights between fighter planes over the Western Front were common, and some pilots became heroes because of their skill. By the end of the war the 'score' (number of enemy aircraft shot down) for the top pilots was Baron von Richthofen (80), Rene Fonk (75) and Mick Mannock (73). But the reality for most airmen was very different. By 1916, many were young men aged 18, who were given a brief training and sent to war. They could expect to live for three weeks. By 1918, the Great Powers were, altogether, using over 10,000 planes at the front line, and over 50,000 airmen had been killed.