The pilot could select 6, 12 or 24. The rockets were carried in a belly pod. This was the only fighter aircraft at the time that had an electronic fuel control system. The system used vacuum tubes, and the best way to test it was to turn the master switch on, hit the start button and at 6 percent rpm, throw the throttle into afterburner. Of course you were really standing on the brakes.
I forgot to mention that it also used the Hughes E-1 fire control radar which told the pilot when to launch.