Machemer served during the 1940 invasion of France and the 1941 invasion of Russia, in which he served as an Unterarzt (medical officer aspirant) of the reconnaissance unit of the 16th Panzer Division. For his part in the latter operation he was awarded the second class Iron Cross. At one point he worked in a captured Soviet hospital, operating on captured Russian soldiers. Whilst in action Machemer was shot in the neck, but after checking it was not serious, returned to duty treating soldiers who had been shot through the lungs. He noted this in a letter home to his wife and Erna's reply was that he "shouldn't consciously put yourself in danger again, it seems to me like a challenge to fate". Helmut also wrote to Erna of his concern that he might be withdrawn from the front line and placed in a field hospital where he would be unlikely to be recommended for a bravery award.