It's locked for the rest of the game. Go the other way.
Other themes would work just as well.
In Mission 001, if I check a security door with a random number and find out that it's locked, does that mean it's locked for the remainder of the game or can I check again in the next operation phase?
Also I just wanted to say how much I'm ejoying this game. I like the multi-layer rules that can be added as you learn the game. One thing I think would be interesting is making this game work with a different theme, like Vietnam. Maybe using a squad or platoon moving through the jungle on patrol or something like that. What do you think?