In theory, this would mean that if there were some sind of crazy prime minister that decided to try and have a military coupye where they get the military on side. The armed forces wouldn't go along with that, unless the queen went along with it as well. So it's a way of separating the government from direct control over the army and the armed forces. It could be a block against a condential sort of facist or whatever,. A kind of safety net, checks and balances.