served during its brief tour of duty with some modest success. Replacement Within the Army research and development community, disputes arose between factions that supported the adoption of the M14 and the 7.62×51mm round from their inception and the other factions that opposed them. The M14 remained the primary infantry rifle in Vietnam until it was replaced by the M16 in 1967, though combat engineer units kept them for several years longer. Further procurement of the M14 was abruptly halted in early 1968 due to a U.S. Department of Defense report which stated that the AR-15, which would soon be designated the M16, was superior to the M14. A series of tests by the U.S. Department of the Army following the report resulted in the decision to cancel the M14, although the DOD did not cancel the previous FY 1963 orders to be delivered. The M16 was ordered as a replacement for the M14 by the direction of Secretary of Defense Robert McNamara in 1964, over the objection of the U.S. Army officers who had backed the M14. Though production of the M14 was officially discontinued, some discontented troops managed to persist with them while deriding the early-model M16 as a frail and underpowered "Mattel toy" that was prone to jamming. A Congressional investigation later discovered these characteristics to be the result of intentional attempts by Army bureaucracy to sabotage the M16's field performance in Vietnam. In late 1967, the U.S. Army designated the M16 as the "Standard A" rifle, and the M14 became a "Limited Standard" weapon. The M14 rifle remained the standard rifle for U.S. Army Basic Training and troops stationed in Europe until 1970. The U.S. Army converted several thousand M14s into M21 sniper rifles, which remained standard issue for this purpose until the adoption of the M24 SWS in 1988. In 1969, tooling for the M14 was sold to Taiwan, and many rifles were exported later to Baltic countries and Israel. Post-1970 U.S. military service Although the M14 was phased out as the standard-issue rifle by 1970, M14 variants are still used by various branches of the U.S. military, as well as other armed forces, especially as a sniper rifle and as a designated marksman rifle (DMR), due to its accuracy and effectiveness at long range. In 1989, the Marine Corps began a program to upgrade their M14s into DMRs. The final product created by the