Alexandr Plaksin mentions the infamous and very dangerous 1982 case (and gives the correct date; the 4th of October, not the 5th) and that nothing other than a UFO almost triggered a nuclear war. (Stonehill)

ABC News Prime Time Live dated October 5, 1995:

Oct. 4, 1982; Soviet Ukraine

6:00 p.m. That day a huge UFO of perfect geometrical shape and 900 meters in diameter hovered over a nearby ballistic missile base. Numerous eyewitnesses confirmed the sighting to David Ensor. So did Lt. Colonel Vladimir Plantonev (we are not certain if this name was spelled correctly by ABC news), a missile engineer. According to him the UFO was a noiseless, disc-shaped craft; it had no portholes, its surface completely even. It made turns, like an airplane would. The missile silo at the base contained a nuclear warhead It was dismantled in the early 1990's. But in 1982 it was fully functional. Plantonev was in the bunker that fateful day in 1982. The room contained dual control panels for the missile, each of them hooked to Moscow. As the UFO hovered overhead, signal lights on both the control panels suddenly turned on, for a short period of time. The lights indicated that the missiles were preparing for launch. Moscow could have initiated such launch, by its transmission of special orders. But no order came from Moscow, and no one at the base pushed any buttons. For 15 long seconds the base simply lost control of its nuclear weapons. Moscow was very much alarmed, and sent an investigation team to verify the incident. A member of the commission, Colonel Igor Chernovshev (we are not certain if this name was spelled correctly by ABC news), corroborated the 1982 incident to David Ensor.

Robert Duvall:

­Even if you remove the US as the target, the incident had repercussions regarding the newly deployed Pershing II missiles. The decision to deploy them was joint US European (NATO). The reasons for these deployments both within the Europe and US strategies need to be ferreted out in total to understand this.