Alexander Graham Bell
Bell was a supporter of aerospace engineering research through the Aerial Experiment Association (AEA), officially formed at Baddeck, Nova Scotia, in October 1907 at the suggestion of his wife Mabel and with her financial support after the sale of some of her real estate. The AEA was headed by Bell and the founding members were four young men: American Glenn H. Curtiss, a motorcycle manufacturer at the time and who held the title "world's fastest man", having ridden his self-constructed motor bicycle around in the shortest time, and who was later awarded the Scientific American Trophy for the first official one-kilometre flight in the Western hemisphere, and who later became a world-renowned airplane manufacturer; Lieutenant Thomas Selfridge, an official observer from the U.S. Federal government and one of the few people in the army who believed that aviation was the future; Frederick W. Baldwin, the first Canadian and first British subject to pilot a public flight in Hammondsport, New York, and J.A.D. McCurdy —Baldwin and McCurdy being new engineering graduates from the University of Toronto.

Q: Which branch of the military was Lieutenant Thomas Selfridge in?
army