No military unit is ever 100% combat ready. Troops will be taking leave, some weapons will be out of commission, there are always some shortages in compliment, authorized slots unfilled, some gear worn or obsolete. So, something less than 100% is as good as you can do.
Back when I was pounding a flight line in USAF, the standard was 71% of squadron aircraft ready to fly every day. We had to report our percent in commission every morning at 4 AM. That gave maintenance most of the night to fix the planes that the pilots had broke flying them the previous day. We had 20 fighters and to make 71% operationally ready, we had to have 15 aircraft in commission, every single morning. We usually had one aircraft in periodic inspection which took days to complete. Or undergoing engine change, which took a day and a half. So we could only afford to have four aircraft down for maintenance after the witching hour of 4 AM.
Aviation Week ran an article this week about readiness rates. Somehow USAF was still making 71%, but just barely. Army, Marines and Navy were only doing 50%. Back in my day, a USAF squadron commander who failed to make 71% got relieved of duty. Dunno how the other services feel about the issue, nowadays.
Distorting the numbers is the huge amount of aircraft out for depot level maintenance (DLM we used to call it). At squadron level we only had to report on squadron aircraft. If we sent an aircraft off for DLM, it no longer counted as assigned to our squadron. About once a year we would send a plane off to depot, and it would take depot a matter of months to get it back to us. So something like 2.5% to 5% of the force was in DLM. That was then
Now, the Marines are reporting 171 F/A18 fighters assigned to squadrons and 109 F/A18 fighters in DLM. That's 38% of the fleet out of commission for DLM. That's bad. Really bad.
Aviation Week (staunch industry supporter that they are) is calling for more funding for aircraft maintenance.
I wonder how you rate the combat readiness of infantry or tank units.