From this encounter with the Viet Cong, the Marine pilots learned that air strikes conducted just prior to a helicopter landing in the heavily populated delta country tended to disclose the location of the landing zone to the enemy. In this instance the Communists had been able to reach the landing zone in the few minutes which elapsed between the last air strike and the arrival of the Marine helicopters. Following this experience, the Marines would no longer allow VNAF air strikes on landing zones prior to operations in the flat delta region.[5-D] [5-D] The development of helicopter tactics and techniques in Vietnam will be covered in detail in a separate monograph being prepared for publication by the History and Museums Division, Headquarters, U.S. Marine Corps. The Americans and Vietnamese, however, soon learned to use fixed-wing aircraft to support helicopter operations in another manner. By mid-June, FARM GATE T-28 Trojans (a single-engine two-seat trainer built by North American) modified to carry bombs, rockets, and machine guns were flying escort missions for the Marine helicopter squadron. This particular aircraft could fly slowly enough to cruise with the HUS yet fast enough to deliver an air strike en route to the objective and then catch up with the helicopter formation. Normally an element of two T-28s accompanied the helicopters and were used primarily to attack targets near the landing zone after the ARVN troops were on the ground. The placement of an American pilot-instructor and a Vietnamese student in the T-28, a requirement imposed by MACV, helped avert language problems which invariably developed when coordinating ARVN ground operations and U.S. air operations. The effectiveness of the escort tactic increased as the Marine and Air Force pilots became accustomed to planning, coordinating, and executing the missions.