We use RCAT in the Krav Maga Force Training Division (Military/Law Enforcement.) It is just an acronym so that it is easier to remember how to break it down and the military seems to love their acronyms.
I generally don’t say RCAT when teaching the civilian classes but I do use those stages.
Redirect the line of fire
Control the weapon (Weight on the weapon)
Deal with the gunman
Disarm
One thing to stress is that the control and attack are as close to simultaneous as you can be.