Colonel Robert W. Gruenhagen was born in Great Falls, Montana on January 20, 1932. He attended high school and joined the Montana Air National Guard on December 5, 1947. After graduation from high school in 1949, he attended the Air Force airplane and engine mechanic course at Sheppard AFB, Texas.

In August 1950, Colonel Gruenhagen was employed as an Air Technician with the Montana Air National Guard with duties as a crew chief on P-51 aircraft.  In March 1951, he was called to active duty with the 186th Fighter Squadron and served at stateside bases with SAC and TAC and overseas with the Icelandic Defense Force. His duties included assignments as flight chief, line chief and quality control inspector.

In January 1953, Gruenhagen returned to technician status with the Montana Air National Guard and was assigned as a crew chief on F-86 aircraft. In December 1954, he was assigned to establish a jet engine maintenance shop and served in this function until May 1958 when he was appointed as Warrant Officer, JG. 

Gruenhagen continued a long and active career in the military – working on numerous aircraft. In November 1978, Colonel Gruenhagen was selected as the Technician Chief of Maintenance. His military duty as the Deputy Commander for Maintenance was assigned on July 12, 1983. He served in this assignment until his retirement in 1987.

Colonel Gruenhagen is a member of the Air Force Association, the American Aviation Historical Society, and the Association of P-51 Historians and Enthusiasts.  He serves as consultant and advisor with matters related to historic aircraft during the Second World War. He is the author of “Mustang – The Story of the P-51 Fighter” and a well-known expert on the P-51.

His decorations and awards included the Meritorious Service Medal, the Air Force Commendation Medal, two Air Force Outstanding Unit awards, the Good Conduct Medal, the National Defense Service Medal, the Air Force Reserve Longevity Award, the Armed Forces Reserve Medal with two hour glass devices, the Expert Marksmanship Medal, the Lone Star Distinguished Service Medal, the Creek Party Service Award, the Texas State Meritorious Service Award and the Texas State Longevity Award. In October 1976, he was presented the Distinguished Service Award by the Confederate Air Force. 

He resides in Kennedale, Texas.  He has two daughters and four grandchildren.