Washington — In the fortunes of the M-16 automatic rifle can be seen the post-World War II fall and rise of the whole US military. A light weapon made of special plastics and alloys, the M-16 was one of the United States Army's many great problems in the Vietnam war. Reliable in prototype, it had been made too fast-firing by military modifications, and it often fouled and jammed during combat.
Today, the M-16 is much improved -- but perhaps still not as good as it should be. The modern version of the rifle wins NATO small-arms reliability trials, but critics complain it is inferior to its Soviet counterpart, the AK-47.
As goes the basic weapon, so goes the US military force.
Like the M-16, the US armed services have been rejuvenated over the past decade. They have better people, a new generation of equipment, and new tactics for the conflicts that strategists say are likely to erupt in today's world.
At the same time, they are troubled by interservice rivalry, expensive weapons that break, and doubts about their war-fighting capability.
``We've gained back what we lost in Vietnam,'' says retired Army Lt. Col. Theodore Crackel, a senior fellow at the conservative Heritage Foundation. ``But we've not gone beyond that to crack through to a whole new way of thinking about the military profession.''
It almost goes without saying that Vietnam was a great trauma for the US military -- and particularly for the Army, which took the brunt of the fighting.
As the war dragged through its decade's course, US arsenals in Western Europe were drawn down to provide materiel for the forces fighting in Southeast Asia. The cohesion of the Army was ripped apart in many units, as the pressure of fighting a controversial war led to high rates of drug use, racial strife, and plummeting morale.
The Army's senior noncommissioned officers (NCOs) -- the tough sergeants who transform recruits into soldiers and anchor solid fighting units -- were almost wiped out in Vietnam. They were replaced by men with a bare eight weeks of training. ``We called 'em shake-'n-bake NCOs,'' recalls Gen. Eugene Meyer, a former Army chief of staff.
Ten years later the Army has finally rebuilt its NCO corps with sergeants who in many ways are more qualified than their predecessors of the early '60s, General Meyer says.
This reflects what a wide range of officers and outside experts rank as the most important change in the military since Vietnam: the higher quality of its personnel.
In 1975, two years after the end of the draft, only 66 percent of first-time enlistees in the US military had graduated from high school. In 1984, by comparison, 93 percent of enlistees had high school diplomas. And the experience level of US forces is increasing, as more of these recruits choose to reenlist.
There are shortages: The Navy doesn't have enough submarine officers, for instance, and the Air Force has a hard time keeping experienced pilots. The services will undoubtedly find recruitment harder in coming years, as the total number of US teen-agers shrinks. But for now, ``it's the best overall personnel status since I've been in the military,'' says retired Air Force Gen. David C. Jones, a former chairman of the Joint Chiefs of Staff.
And these soldiers, sailors, and airmen are better trained than they were 10 years ago. The Air Force, troubled by a relatively poor performance in Vietnam (two North Vietnamese MIGs shot down for each US plane lost, compared with a 10-to-1 loss ratio during the Korean war) now puts pilots through more realistic dogfight training, such as the Red Flag exercises held at Nellis Air Force Base in Nevada.
The Army, for its part, has taken some 160,000 soldiers through the National Training Center at Fort Irwin, Calif. There, on a desert battlefield the size of Rhode Island, soldiers play war with low-power laser weapons and computers that register ``kills.'' Much of this training is aimed at familiarizing military personnel with a new generation of complicated conventional weapons.
During the 1960s and early '70s, as millions of dollars went for munitions and other war supplies, the Pentagon had to defer many weapons-modernization projects. ``Vietnam cost us a decade of defense modernization,'' says Robert Komer, an undersecretary of defense during the Carter administration.
But by the early years of the Reagan administration, modern weapons long coveted by the military were finally arriving in quantity. The Army has received congressional approval for 4,223 M-1 turbine-powered tanks; the Air Force will soon have purchased a combined total of almost 2,000 F-15 and F-16 tactical fighters. Bradley fighting vehicles equipped with TOW antitank missiles, AH-64 Apache helicopters, and the controversial Aegis missile cruiser are coming on line.
For the most part, these weapons systems will replace worn-out '60s-vintage equipment, such as the M-60 tank. As a just-released Congressional Budget Office reports point out, only the Navy is becoming a substantially larger force under President Reagan, as it steams toward a planned goal of 600 ships by 1989.
The Army can now deploy 17 active-duty divisions, up from the 16 it had between 1976 and '84. The Air Force went from 74 tactical squadrons in 1976 to 78 today.
While the modern generation of microchip-laden weapons will add punch almost undreamed of in the '60s to US forces, it is also very costly. An F-15, for instance, is three times as expensive as its predecessor, the F-4 Phantom -- even after adjusting for inflation.
Congress has long debated the virtues of quality vs. quantity when drawing up the defense budget. In coming years, suggests a CBO analysis, this debate will become much sharper. If current cost trends continue, for example, it may ``be almost impossible to maintain the current 36-wing [tactical air] force in the next century -- let alone expand it,'' the CBO report concludes.
This means the traditional American way of waging conventional war -- rolling back opponents with sheer weight of materiel -- is sure to change.
Next: how US military tactics are changing. Graph: First time enlistees with high school diploma 1975 66% '76 69 '77 69 '78 77 '79 73 '80 68 '81 81 '82 86 '83 89 '84 93 Source: US Defense Department