The attack of the 1st Marines, originally scheduled for 0500 on 13 September, had been changed to 0900 by Division orders. One reason for the postponement was the serious shortage of ammunition and other supplies after the urgent demands of the last two days. Another reason was the inability of VMO-6 helicopters, lifting two wounded men at most, to cope with the mounting casualty lists. Enemy interdiction of roads added in several instances to the complications of a major logistical problem, particularly in the zone of Lieutenant Colonel Franklin B. Nihart’s 2d Battalion, 1st Marines. The hour had struck for HMR-161, and the world’s first large-scale helicopter supply operation in a combat zone would soon be under way. It was not the development of a day. On the contrary, its roots went all the way back to 1945, when the atomic bomb of Hiroshima rendered obsolescent in 10 seconds a system of amphibious assault tactics that had been 10 years in the making. Obviously, the concentrations of transports, warships, and aircraft carriers that had made possible the Saipan and Iwo Jima landings would be sitting ducks for an enemy armed with atomic weapons. The problem was left on the doorstep of the Marine Corps Schools, which had reared the Fleet Marine Force from infancy to maturity during the 1930’s. A Special Board and Secretariat were appointed for studies. They assigned two general missions to Marine Helicopter Experimental Squadron 1 (HMX-1), organized late in 1947 before the first rotary-wing aircraft had been delivered. These missions were: (1) Develop techniques and tactics in connection with the movement of assault troops by helicopter in amphibious operations; (2) Evaluate a small helicopter as a replacement for the present OY type aircraft to be used for gunfire spotting, observation, and liaison missions in connection with amphibious operation.[282] [282] CMC ltr to CO MCAS, Quantico, 3 Dec 47. The second mission resulted in the small Sikorsky and Bell helicopters of VMO-6 which landed in Korea with the 1st Provisional Marine Brigade in August 1950. Although it was originally believed that rotary wing aircraft might replace the OYs, combat experience soon demonstrated that the best results were obtained by retaining both types in fairly equal numbers. Landing exercises under simulated combat conditions were conducted by HMX-1 in fulfillment of the first mission. At first the squadron had only three-place helicopters. Later, when the usefulness of the helicopter was fully realized, even the new 10-place “choppers” were never available in sufficient numbers. The capacity designations of these machines, however, were more ideal than real, for the helicopters could lift only four to six men in addition to the pilot, copilot, and crewman. Despite such drawbacks, HMX-1 developed tactical and logistical techniques for helicopter landings to be made from widely dispersed carriers against an enemy using atomic weapons.