At Edwards Air Force Base in California, Colonel Shaefer reached Mach 1 in 1950 in a McDonnell XF-88 Voodoo in a steep dive while testing the jet fighter.

Assigned in 1947 to what is now Wright-Patterson Air Force Base in Ohio, he was in a group of test pilots that included Chuck Yeager, who first broke the sound barrier that year. Later, as the chief of the operations test flight test division, Colonel Shaefer later became Yeager's superior.

Born a twin in Lansing, Michigan, he was raised in Albuquerque and enrolled at the University of New Mexico. Both twins dropped out to enlist in the U.S. Army Air Corps in 1939.

His brother went on to West Point while Colonel Shaefer did flight training. He served in North Africa and Italy and participated in the low-level bombing of the German-held oil refineries at Ploesti, Romania. He flew 15 missions over Ploesti, and among his honors were the Distinguished Flying Cross and six awards of the Air Medal.

After the war ended, Colonel Shaefer graduated from the University of Southern California where he mixed with fellow pilots Errol Flynn, Howard Hughes and Peter Lawford. He soon left Hollywood for Ohio, where he became a test pilot.

After an assignment in Sweden, Colonel Shaefer worked in the Strategic Air Command in California and in 1959 was posted to the Pentagon. Assigned to the Joint Chiefs of Staff at one point, he prepared and gave a three-hour briefing on the general nuclear war plan to President John F. Kennedy in the White House.

Subsequent assignments took him to NATO Defense College, the Allied headquarters in Paris and the NATO Military Committee in Washington, where he was on loan to the Transportation Department as an expert in high-speed aircraft. He retired in 1968 at the rank of Colonel.

In retirement, he became president of a sport equipment company, Leisure Time Specialists.

He owned racehorses and enjoyed playing golf.

His marriage to Shirley Anne Hawkins ended in divorce. His second wife, Berta Lucia Castillo, died in 2003.

Survivors include three children from his first marriage, Stephanie Lynn Shaefer of Alexandria, Virginia, retired Army Lieutenant Colonel Michael Kent Shaefer of Alexandria and retired Air Force Colonel Jeffrey Rowland Shaefer of Hingham, Massachusetts; and two grandchildren.

He is survived by Michael Kent Shaefer and Stephanie Lynn Shaefer both of Alexandria, Virginia and Jeffry Rowland Shaefer of Hingham, Massachusetts. He is also survived by his daughter-in-law, Peggy Lowney Shaefer and two grandchildren, Sam and Bridgit Shaefer, also of Hingham, Massachusetts.

Family and friends will honor and celebrate his life on Thursday, November 20, 2008, at 1 p.m. at The Old Post Chapel at Fort Myers with interment to follow at Arlington National Cemetery. A reception will follow at 3 p.m. at The Army Navy Country Club. In lieu of flowers, please donate to your favorite charity.