In 1946, U.S. Marine General Roy S. Geiger observed the atomic bomb tests at Bikini Atoll and instantly recognized that atomic bombs could render amphibious landings difficult because of the dense concentrations of troops, ships and material at beachheads. During this time, The Commandant of the Marine Corps, Alexander Vandegrift, convened a special board known as the Hogaboom Board. This board recommended that the USMC develop transport helicopters in order to allow a diffused attack on enemy shores. It also recommended that the USMC form an experimental helicopter squadron. HMX-1 was commissioned in 1947 with Sikorsky HO3S-1s. In 1948 the Marine Corps Schools came out with "Amphibious Operations—Employment of Helicopters (Tentative)", or "Phib-31", which was the first manual for helicopter airmobile operations. The Marines used the term vertical envelopment instead of air mobility or air assault. HMX-1 performed its first vertical envelopment from the deck of an aircraft carrier in an exercise in 1949.