and Kawasaki in Japan. Operational history Vietnam War The Army finally settled on the larger Chinook as its standard medium-transport helicopter, and as of February 1966, 161 aircraft had been delivered to the Army. The 1st Cavalry Division had brought its organic Chinook battalion (three Chinook companies) when it arrived in 1965 and a separate aviation medium helicopter company, the 147th, had arrived in Vietnam on 29 November 1965. This latter company was initially placed in direct support of the 1st Infantry Division. CH-47 crews quickly learned to mount an M60 machine gun in each of the forward doors. Sometimes they also installed an M60 or M2 machine gun to fire from the rear cargo door. The most spectacular mission in Vietnam for the Chinook was the placing of artillery batteries in perilous mountain positions inaccessible by any other means, and then keeping them resupplied with large quantities of ammunition. The 1st Cavalry Division found that its CH-47s were limited to a payload when operating in the mountains, but could carry an additional when operating near the coast. The early Chinook design was limited by its rotor system which did not permit full use of the installed power, and users were anxious for an improved version which would upgrade this system. As with any new piece of equipment, the Chinook presented a major problem of "customer education". Commanders and crew chiefs had to be constantly alert that eager soldiers did not overload the temptingly large cargo compartment. It would be some time before troops would be experts at using sling loads. The Chinook soon proved to be such an invaluable aircraft for artillery movement and heavy logistics that it was seldom used as an assault troop carrier. Some of the Chinook fleet was used for casualty evacuation, and due to the very heavy demand for the helicopters, they were usually overburdened with wounded. Perhaps the most cost effective use of the Chinook was the recovery of other downed aircraft. At the Vietnam war's peak the US Army had 21 Chinook companies in Vietnam. Pilots discovered the CH-47A's transmission system could not handle the two gas turbines running at full power, and high humidity and heat reduced the maximum lift by more than 20% in the low lands and 30% in mountain areas. More powerful, improved transmission and strengthened fuselages arrived in 1968 with the CH-47B, followed a few months later