While many are quick to highlight the U.S. Air Force B-52 bomber as an example of military hardware in-service longevity, the Army is no stranger to milking decades of life out of hardware designs that are upgraded rather than replaced. An excellent example of this can be seen in the M2 .50-caliber machine gun, which in 2013 marked the 80th anniversary of its initial 1933 service entry. More recently, Army planners have suggested that the service will continue to enhance and maintain the viability of its M1 series Abrams main battle tanks until possibly 2050, which would mark an impressive 70 years since that original introduction.

Although still decades short of octogenarian or even septuagenarian milestones, the M16 5.56 x 45 mm (5.56 NATO) rifle has reached a half century of service since its initial introduction in 1963. While the current variants like the M16A2/M16A4 represent the modern generations of the full-length combat rifle, the M16 design has also spawned the M4/M4A1 carbine models that are a ubiquitous presence in U.S. combat operations.

The M16 is hardly the first U.S. Army rifle to draw criticism. In fact, according to a June 1, 1968, “History of the M16 Weapon System” prepared for the Army Chief of Staff by the M16 Rifle Review Panel, the M16 was one of three of the eight “rifles” adopted by the U.S. Army as standard since the Revolutionary War that has been “the subject of great controversy” – the other two being the Krag-Jorgensen and the M1 Garand.

While the M16 weapon system has reached its 50-year milestone, however, not all users or observers view it in a “golden” light. Early combat experiences with the M16 in Vietnam, for example, prompted the Army to conduct a formal survey of users in June 1968. Even today, with approximately half a million product improved M4/M4A1 carbine models in U.S. inventories, the weapons and their underlying ballistic performance are drawing public criticism.

The M16 is hardly the first U.S. Army rifle to draw criticism. In fact, according to a June 1, 1968, “History of the M16 Weapon System” prepared for the Army Chief of Staff by the M16 Rifle Review Panel, the M16 was one of three of the eight “rifles” adopted by the U.S. Army as standard since the Revolutionary War that has been “the subject of great controversy” – the other two being the Krag-Jorgensen and the M1 Garand.

The report stated that “A review of the history of American rifles will show that the U.S. Army before World War II did not take advantage of the latest improvements in weaponry before adopting a new rifle,” and pointed to feasibility studies conducted during the period 1946 to 1950 to meet a stated U.S. Army requirement for a lightweight automatic rifle. A prototype M14 emerged from feasibility studies of 10 different rifle designs and was subsequently “tested competitively against the Belgian Fabrique Nationale (FN)” FAL from 1952 to 1956.

“The development of the M14 rifle, of course, was restricted to the standard 7.62 mm (caliber .30) NATO round, which had been adopted in 1953, thus all but precluding the development of a truly lightweight weapon,” the report added.

The M14 rifle was finally developed and standardized in 1957. But even during this standardization process, design work was already under way on a new rifle design initially called the AR15 and later XM16E1 and M16A1.

U.S. Army discussions of a small-caliber, high-velocity round actually began in 1928 with a series of recommendations that emerged from the so-called “Pig Board” (named for the live targets used in some of the testing) that had investigated projectiles in caliber .30, .276, and .256.

Among the board recommendations was the adoption of caliber .276 and the development of a semi-automatic rifle in that caliber. However, the recommendation foundered in the wake of Army Ordnance Department opposition to a new cartridge and the subsequent adoption of the .30-06-caliber M1 Garand.

According to the 1968 service history, it was nearly a quarter century later, in 1952, before the U.S. Army Ordnance Corps began seriously investigating the application of high-velocity, small-caliber cartridges in rifles and carbines.

By 1955, the U.S. Continental Army Command (USCONARC) Board 3 (“The Infantry Board”) “conducted an evaluation of an M2 carbine that had been modified to fire a high-velocity caliber .22 cartridge. The report of the project recommended that investigation of the high velocity, small caliber principle be given a high priority and that a lightweight rifle utilizing the high velocity, small caliber concept be developed.”

In late March 1957, USCONARC directed the Army Infantry Board to prepare a list of the required military characteristics for a high-velocity, small-caliber rifle, with those requirements quickly prepared and forwarded back to USCONARC for approval in late July.

However, even as this process was under way, the report notes that Gen. Willard C. Wyman, then-commanding general of USCONARC, “acted to expedite the development of a lightweight rifle” through a “verbal request” to Eugene Stoner of the Armalite Corporation, as well as to other gun manufacturers. That request process initiated the development of the AR15 rifle in mid-1957.

“The request, also made to other gun manufacturers, was for a new lightweight infantry rifle chambered for high velocity caliber .22 cartridges,” the history notes. “The general specifications were: a maximum loaded weight of six pounds; a capability of firing semiautomatic or full automatic; a killing power equal to or better than that of the M1 (Garand) rifle up to 500 yards; and a capability of penetrating a steel helmet or standard body armor at 500 yards.”

Prototype designs were developed by both Armalite (caliber .223) and Winchester (caliber .224 Winchester).

The AR15 that was delivered for testing by the U.S. Army Infantry Board in 1958 was characterized as a scaled-down version of the 7.62 mm AR10 rifle, which had also been designed by Stoner.

The early test results of the lightweight designs were reported to be positive and added fuel to an increasing number of debates already complicated by the 1953 NATO agreement to standardize the 7.62 mm. In fact, in late 1958, a board of general officers called the Powell Board was convened to review the Army’s rifle program.

While the board reportedly “liked” the small-caliber, high-velocity concept, it recommended that “no further consideration be given to the caliber .223 round.” Further, the Powell Board reportedly estimated a .258 caliber as the optimum small-caliber round and recommended that development of an AR15 type of weapon, chambered for caliber .258, be expedited to replace the M14 in the rifle role.