Fail-Safe (1964)

Watching this film is much like watching a stage play, onto which an assortment of freebie special effects have been added by people who care not a jot! I would guess in truth that the budget was peanuts judging by the quality of this stuff. The play itself is very well written and performed, full of tension. If you come to this film expecting spectacular action scenes with impressive and expensive special effects, the stock footage of fighter aircraft (shown in the negative print presumably to disguise their true appearance) doing things not being described in the dialogue (firing missiles when they're supposedly going to afterburners, etc) will cause you to scoff and turn off! But look away from those moments and concentrate on the main show and the tension overwhelms.