TOMORROW at 10 a.m., at Warren Air Force Base in Cheyenne, Wyo., the last MX missile will be "deactivated," and a turbulent chapter of history will come to an end.
The MX is hardly remembered now; its phase-out began without fanfare four years ago. But in the late 1970's and the '80s - at the height of the United States-Soviet nuclear arms race, amid tensions over the invasion of Afghanistan and the collapse of détente - the MX was the centerpiece of the American military buildup, the object of longer and fiercer debates than any other weapon in modern times.
"It was a defining symbol of an era," says John Pike, director of GlobalSecurity.org. "For its supporters, it was 'peace through strength.' For its opponents, it was 'the mad momentum of the arms race.' Both sides cared about it so much. Now it's going out, and nobody even notices."
It was the biggest intercontinental ballistic missile the United States ever built - 71 feet long, 7 feet, 8 inches in diameter, 195,000 pounds, tipped with 10 nuclear warheads, each sufficiently powerful and accurate (at least in theory) to blast apart a concrete-hardened Soviet missile silo. (Its predecessor, the Minuteman III, held only three, less potent warheads.)
In the mid-1970's, the Air Force saw a growing threat from Moscow. The Soviets were deploying their own monster missile, the SS-18, which could fling 10 large warheads at separate targets. Many worried that enough SS-18's could destroy all our ICBM's in a first strike. With the MX, we could pose the same threat to their ICBM's.
But many arms analysts argued that the MX would be "destabilizing." If the United States and the Soviet Union both had missiles that could launch a first strike and were at the same time vulnerable to a first strike, then both leaders might feel tempted to attack - if just to pre-empt the other side from doing so.
In 1976, Congress, concerned over this mutual vulnerability, passed a bill blocking money for any new ICBM that would be based in a fixed silo. Over the next couple of years, the Air Force proposed 40 different plans to make the MX missiles mobile, so the Soviets would have a harder time hitting them. The ideas included flying them around on C-5 cargo planes, shuttling them in railroad cars, trucking them down highways, and moving them through tunnels from one silo to another as in an elaborate shell game.
In September 1979, President Jimmy Carter approved the shell-game concept. His plan called for 200 MX missiles, each flitting back and forth among 23 silos. The idea was that the Soviets would have to fire 23 warheads to ensure hitting a single MX - 4,600 warheads to get them all - a task so onerous they wouldn't bother.
The debate took off at full throttle and stayed there for a decade. It was an unusually technical, almost metaphysical debate, with each side drawing up charts and graphs displaying "deterrence gaps," "missile throw-weight ratios" and "comparative hard-target-kill probabilities."
Representative Barney Frank, Democrat from Massachusetts who was a leading MX opponent in those debates, recalled: "You showed your credentials by being able to talk about all this detail, but a lot of people - including Democrats - got sucked into it. They learned the lingo, but they forgot it had no relation to reality. It was like critics of 'The Three Stooges' debating the right way to squirt seltzer up your nose. They forgot that the whole thing was a little silly."
Mr. Frank and a growing number of skeptics asked: Was ICBM-vulnerability really a big problem? Most American nuclear missiles were on submarines, which were undetectable and therefore invulnerable to attack. And did those charts mean anything? Would a Soviet leader really risk a first strike - launch thousands of warheads, killing as many as 20 million Americans from fallout alone - on the basis of theoretical calculations? Would an American president decline to retaliate? With both sides possessing thousands of warheads, how would either have an advantage?
When Ronald Reagan became president in 1981, he abandoned Mr. Carter's mobile plan and decided to put the MX's in silos. Air Force commanders had never been keen on the expensive shell game; they just wanted big new missiles to keep up with the Soviets'. And Republicans from Western states didn't want to turn vast stretches of their land into missile trenches, much less ground zero for atomic Armageddon.
In 1983, the White House and Capitol Hill compromised: the MX would be put in silos, but the Air Force would build 500 single-warhead, mobile ICBM's, called the Midgetman. The idea made little sense. The MX would still be the Soviets' prime target, and would still be vulnerable.
By the time Reagan left office, the MX program was halted at 50 missiles, not enough to counter the Soviets' SS-18's. The Midgetman was never built.
In the end, tangible diplomacy trumped abstract strategy. A new Soviet leader, Mikhail Gorbachev, emerged as a Western-leaning reformer. Reagan, the veteran anti-Communist, pronounced him trustworthy. Relations warmed. Arms treaties were signed, armies demobilized. The calculations of throw weight and first-strike probabilities looked as gloomy as ever, but nobody cared - and almost nobody minded that nobody cared. They didn't seem quite so real anymore.
Herman Kahn said he wrote his 1960 tome "On Thermonuclear War" "to create a vocabulary" in which the subject could be discussed "comfortably and easily." The 1980's were a truly frightening time. The alluring esoterica of the MX debate, which drew heavily on Mr. Kahn's vocabulary, offered the comforting appearance that even the ghastliest prospect, nuclear war, could be grasped and controlled.
Did the MX help win the cold war? Arnold Punaro, a retired Air Force major general who was the Senate Armed Services Committee's staff director in the 80's, says he thinks so. "The forts that we now go visit as museums were the MX missiles of their day," he says. "They preserved our defenses, deterred attacks."
Others are skeptical. Reagan's missile-defense program may have played a role. Kremlin archives reveal that Mr. Gorbachev feared that it might work and that the Soviet Union would go bankrupt trying to keep up. But there's no evidence, yet, that he feared the MX.
Either way, General Punaro says the real question concerns the future. He notes: "We're vulnerable today to a chemical, biological or radiological attack by terrorists. What is our concept of deterrence against that?"