Late in 1940, Henry Gerecke's son Hank enlisted in The U.S. Army. Just a year later in December 1941, Japan attacked Pearl Harbour and the United States joined The Second World War to fight alongside Britain and the other allied forces against the axis powers. Corky followed his older brother's example by joining the army in September 1942 while Henry Gerecke continued his work at City Mission. In June 1943 Henry Gerecke followed his sons to war and volunteered as an army chaplain. By August, Gerecke was already underway with his month of training at The Chaplain School at Harvard University following which he was promptly deployed to Hermitage in Southern England with the U.S. Army's Ninety-Eighth General Hospital, a hospital that received injured soldiers from the front-lines of The Western Front. After VE day the Ninety-Eighth were no longer required in England so along with Gerecke as their chaplain went to Munich, Germany to re-establish a damaged hospital in the war-torn German city.