MG Cairns was born to a career Army doctor, lieutenant-colonel Douglas Walker Cairns and his wife, Ethel Moore Cairns, on February 14, 1910, in Brooklyn, New York. His father, LTC Cairns went on Active Duty during the First World War, beginning over 100 years of unbroken Active Duty Service among his descendants. Dr. Cairns was with Gen. John J. "Blackjack" Pershing during the Pancho Villa expedition and subsequently at Governor's Island, New York. Bugs Cairns and his brother, COL (Army Air Corps and USAF) Douglas Moore Cairns, graduated from West Point in 1932 and 1933 respectively. Cairns was named for two of his ancestors, Brigadier General Robert Bogardus, who had been in charge of the defense of New York during the War of 1812, and his great uncle, Colonel Robert Bogardus Snowden, who had been the tip of Longstreet's spear at the Battle of Chickamauga during the Civil War. He was descended from Captain Robert Walker, an officer in the American Revolution, as well as Lieutenant James Frisbie, who lost his life under the command of John Paul Jones on the Bon Homme Richard in the engagement with the Serapis. He was descended from Dominie Everardus Bogardus, the first Dutch Reformed pastor in New Amsterdam who arrived in 1634, and Isaac Snowden, one of the treasurers of the Continental Congress and the Treasurer of the City of Philadelphia.