Crimson Tide (1995)
The crucial dramatic plotline of this film is; that without the authorization, and the validated order to do so; and, with such authorization and order being in doubt; and, not being positively and affirmatively known; and, not being in the possession of the submarine's commanding officer and its qualified nuclear weapons officers; the commanding officer (Hackman) proposed; (and his submarine had the capability to); arm and launch the nuclear weapons of his boat, on his and his officer's decisions alone, to do so.
Unknown to the American public generally, at the time, and wrongly presumed to in fact be wholly otherwise; this allegedly fictional sequence of events was in fact true. The commanding officers and the nuclear weapons officers of the ballistic missile submarine force; unlike their Air Force counterparts in the then existent Strike Command (the legendary Strategic Air Command (SAC) was abolished in 1992), had in effect independent launch authority; should the officers of the submarine agree to such an action.
The complete nuclear weapons release protocol (i.e. the permissive action links to arm and launch), existed entirely aboard the sub and in the training of its crew, and the equipment and systems they were provided.
For the land based missiles and bombers this was not the case. The launch order transmitted by the "football" carrying military aide to the President, for the bomber and land based missile forces had to transmit to those forces, the unlocking codes necessary to initiate the weapons' arming and release (launching) protocols. Without this, the missiles could both never be launched, and their weapons never armed. It was known as positive control.
Because of the difficulty of communicating with the subs, at all times on deterrent patrol, and normally several hundred feet beneath the ocean's surface; and also normally operating in total radio silence; a crisis might develop, and the ground based radio's to communicate with the subs might be preemptively destroyed. So the Navy and Defense Department's initial solution; was, to give launch control authority jointly and individually to the sub's commander and his officers.
This was not generally known until "Crimson Tide". With the reduction in global tensions since the 1990s, between the superpowers; and, the vast improvement in ground and space based global communications, the US Navy's "boomers" are now joined in the positive control regime with the other legs of the nuclear triad.