On a Royal Artillery course in Anglesey in 1960 or thereabouts, we were being taught how to use a SAM called, I think, Thunderbird. Was it semi-passive? I believe so but could be wrong.
The course culminated in an exercise involving assessing an incoming threat and deciding when to launch and what at.
This was done, to save money, with a large sort of double-sided easel which allowed a talc board, marked up as a radar screen, to be passed from one side to the other over its top.
A WRAC stood on one side and plotted 3 targets, passed the board over to the trainee who assessed the targets and passed it back. The WRAC then replotted the targets and passed it back; it was assessed and passed back, and so on as the enemy drew nearer on the plot.
Some people were adept at writing upside-down messages to the WRAC, but this was frowned on.
This pleasurable game continued until the trainee gave the command to launch the SAM.
At this point the WRAC appeared on the trainee side with a bag containing 10 balls.
7 were black, and 3 were white, and if you picked a white one you had killed your target.
This was because the known probablility of an otherwise perfect shoot actually killing the target was 30%.