Without this key, the firing of U.S. missiles cannot happen. On the Russian side, the process cannot begin unless an unlocking code from higher authority is received and entered into the fire control computer network. It is frankly inconceivable that a computer glitch could be responsible for executing all the steps involved in this count-down for launching submarine missiles. The scenario is almost as bizarre as one in which a computer malfunction by itself causes nuclear weapons to be loaded onto bombers, the bombers to take off, to fly half way around the globe, and to drop their payloads. People, not computers, dominate both bomber and submarine operations.
Scenarios involving some other types of nuclear weapons are harder to dismiss out of hand.
Control of the missiles is highly automated. The launch process is far less labor intensive. The missiles are fueled, and their gyroscopes are spinning. They are ready to fly. Russia's land-based rockets can even be launched by remote computer instructions sent from command posts in Moscow, bypassing the human operators down the chain of command.