John H. Gravestock was born November 5, 1918 in San Francisco, California to Frank G. and Maude R. (Lamb) Gravestock. There were four children in the family. His father worked for the Mountain States Telephone Co. In the 1920 U.S. Census, the family was living in Trinidad, Colorado. By 1935 the family had moved to Denver, Colorado.

Gravestock graduated from the University of Colorado in 1941. In April 1941, Gravestock enlisted in the United States Army Air Corps from Denver County, Colorado. He was commissioned in December 1941 at Mather Field in California. Service Numbers 18045662 and O-432056. 1LT Gravestock served with the 154th Observation Squadron, 68th Observation Group.

On February 26, 1942, Gravestock married Barbara Holmes in Savannah, Georgia. Barbara was from Boulder, Colorado.

In May 1942, 1LT Gravestock was deployed to England with the First Pursuit Squadron, Night Fliers. The 154th Observation Squadron was deployed to Bilda Airdrome in Algeria in early November. They moved to Oujda airbase in French Morocco in December.

On December 16, the squadron completed the first operational combat flight. On January 7, 1943, the 154th Observation Squadron had its first combat casualties. An A-20 Havoc with a crew of CPT Clyde A. Knapp, 1LT Gravestock, SSGT William F. Pozzi and PFC Edward H. Reynolds went missing in action. The plane and crew were not recovered. The men were declared dead in January 1944.

John H. Gravestock is memorialized in North Africa American Cemetery and Memorial in Tunisia.

1LT Gravestock was posthumously awarded the Purple Heart in June 1943.