With reference to a question Are there still any companies/academic centers that use mainframes from 60s-70s? on Programmers stack exchange, I answered mentioning the following:
When I was working at RAF Filingdales in the mid 90's, on the Ballistic Missile Early Warning System there, we were told that they couldn't directly connect anything but the original mainframe to the radar array, as it would be considered a violation of a strategic arms treaty governing the use of the early warning radar system.
My assertion was challenged by a commenter who suggested it was the radar itself which was limited by SALT, so it seems that I'm not the only person who has been told that early warning systems are controlled by international treaty.
A survey of the appropriate wikipedia pages doesn't appear to mention either radar warning systems or the computers connected to them in relation to any of these treaties. The closest thing I can find is the Anti-Ballistic Missile Treaty but this appears to be about the missiles used to shoot down Ballistic Missiles rather than the tracking systems used to locate incoming missiles.