In ordinary times, Moscow’s control over its roughly 30,000 warheads is tighter than the reins on the American nuclear arsenal. Under a system designed in the early 1980s, no single person can launch strategic weapons. To begin the process, a special military unit assigned to the president helps him generate a secret code. At the same time, the defense minister must generate his own launch code. Neither code will suffice for a launch. Both are transmitted to the Soviet General Staff’s Main Operations Directorate. Using computer algorithms, the directorate electronically combines the two to produce a 12-digit number that is encrypted, then fed on a special secure frequency to ICBM silos or ballistic-missile submarines.

There are further safeguards. No single code works on all Soviet strategic systems. The president and defense minister must repeat the process to launch groups of missiles. And in submarine-based systems, a launch can be executed only with the approval of a political officer who receives his verifying code on a different channel from the vessel’s captain and executive officer. But such highly centralized control may increase the danger in situations like last week’s putsch, U.S. weapons analysts say. With Defense Minister Dmitry Yazov on board, coup leaders controlled both codes needed to send a launch order down the chain of command. It could still be thwarted on site, however-an increasing possibility with the armed forces as factionalized as they now seem to be.

But another feature of the Soviet command system could have enabled the coup leaders to bypass dissident elements. In interviews with Soviet officers, Brookings Institution arms expert Bruce G. Blair has learned that Moscow has an alternate launch process. The Soviet General Staff has special bunkers with communications equipment that can bypass missile crews. The president and defense minister enter their launch codes into the command bunker’s computer, and the bunker can send a signal by radio or cable to launch certain missiles with no on-site operation. This automatic launch system is set up for some of the newer Soviet missiles like the Soviet SS-17, SS-18 and SS-19, Blair says. “The launch crews can essentially go to sleep,” he explains. “The missile in the field can be set on automatic, then fired by remote control through a keyed transmission from the central command post.” Blair suspects that even some submarines have such a system.

The Pentagon refuses to comment on this automatic launch system. But its knowledge of the top-down method of Soviet nuclear control added urgency to surveillance of Soviet nuclear forces during the three-day coup. Reassuringly, the activity was routine. The National Security Agency picked up no unusual radio traffic between the Soviet Army’s General Staff and the Soviet Strategic Rocket Forces that man more than 1,300 land-based ICBMs, of which about 70 percent remain on full combat alert at any time. Soviet ballistic-missile submarines on patrol received only routine communications from headquarters, Soviet strategic bombers, normally not on alert in peacetime, remained in their hangars. And there were no reports of any of the tactical nuclear weapons being moved or activated.

Even at the height of the crisis, there was no evidence that a new conservative Soviet regime would have been any more inclined to launch nuclear weapons than the legitimate one. Just a week before the attempted coup, one of the Soviet generals who backed it had asked Gen. Colin Powell, chairman of the Joint Chiefs of Staff, to arrange a meeting to consider new measures to safeguard nuclear arsenals. Still, the situation was frightening. “No matter what the regime might have been, we’re talking about people who were on the brink of physical collapse,” Blair says. “They may behave irrationally.” The real danger could have been nuclear blackmail: the putschists using their possession of the launch codes as leverage. But that was perhaps too much for the Kremlin hard-liners with their fingers briefly on the button.