He was a Petty Officer (equiv) on SMS Seydlitz during the Battle of the Dogger Bank in January 1915. During the battle, the ship was hit by gunfire from HMS Lion that knocked out both rear turrets and caused a cordite flash-over. Heidkamp prevented his ship from exploding by flooding the magazines. He turned the valves even though they were glowing red-hot. During this action his hands and lungs were severely injured, and he would die of consequent lung disease in 1931.
After his recovery Heidkamp continued to serve on SMS Seydlitz until its scuttling in Scapa Flow on 21 June 1919. Thereafter Heidkamp became a British prisoner of war, from which he returned to Germany in 1920. After the war Heidkamp took over his father's grocery store in Untereschbach. Heidkamp was married and had four children.
- Fritz-Otto Busch, Deutsche Seekriegsgeschichte (1936)