In 1941 he and Don McNeil won the National Indoor Doubles Championship, defeating Jack Kramer and Bobby Riggs in the final.

Also in 1941, he partnered with Bobby Riggs to win the River Oaks Doubles Championship, beating Jack Kramer and Ted Schroeder in the final.

[3] In 1946 he and Don McNeil successfully defended their National Indoor Doubles Championship, this time defeating Pancho Segura and Alejo Russell in the final.

In April 1941 Guernsey signed up for the United States Army Air Force (USAAF) and was sent to California for fighter pilot training.

In 1944 Guernsey was transferred to the 8th Air Force in England where he flew support missions for bombing campaigns and was credited with shooting down two German enemy planes.