I went through the 91-94 drawdown in the AF. On the officer side they had to slash mostly O-3s and below. They first riffed all the reserve officers, which was about a third. Then they went after the prior enlisted with 20 years or more with the SERB. Then they reduced the promotion % to Major.
That was still not enough, they waived the service committal for Academy grads and others. They even had a limited 15 year retirement. Personnel has many management tools available to accomplish the downsizing, most are not pretty.
and it is always the OCS grads that take the first hit, not the Professional Officers that went to West Point and then rarely left stateside.