Hoisted from comments, Brad de Long-style. I’ve taken the liberty of slightly editing some comments by reader Buffpilot that might help one understand where some of the costs of operating the military go. His comments focus on bombers.
Training: B-2 bomber pilots get two sorties/month in the B-2. They also get time flying T-38 trainers and fly one of the most realistic combat simulators around. The B-52/B-1 pilots fly 4-5 sorties/month but have crappy simulators and no T-38s. Costs per flying hour go on a ratio of 1/2/6 (B-52/B-1/B-2). The B-1 and B-52 costs would be roughly the same, but the B-1s still practice low-level flying which beats the planes up more and sucks down a lot more gas/hour. B-52s fly high only and by one measure costs roughly $20K/hr to fly in 2000 (how you calculate this number varies widely but the ratios stay the same). B-2 costs are almost totally due to keeping them stealthy. The B-2 actually reports two MC rates, one with stealth and one without, and the numbers you see above (33% with stealth, 80% without) haven’t change since I was tracking it in the pentagon in 2000. All the bomber units sit around an 80% readiness rate at any one time.
Readiness: All the bombers are on a 5 year rotation for depot-level maintenance. Thus roughly 2-3 B-2s are always ‘in the shop’ (as are, for example, 7-9 B-52s). 1-2 will be out constantly for MX training and base-level modifications/maintenance (but can come up quickly). Of the rest a certain % will be kept at the highest readiness level for quick reaction tasking, the 33% mentioned above, i.e. 6-7 aircraft, the rest of the fleet will be used for your day-to-day pilot training. They will churn the aircraft through all these activities to maintain and even wear on the planes.
Crew: The bombers are only manned at a 1.2 crews/plane. Over Afghanistan that meant a time line for a B-52 crew would look like this. Takeoff fly 16 hour mission and land. 3 hours postflight (debrief, mx, etc). Then roughly 36 hours off time, show 3 hours prior to takeoff and repeat. For months. It was very tough on the flyers and beat them up. On the plus side no one could really shoot at you, though we did loose a B-1 due to a nighttime electrical malfunction.
Use: The B-2s have seen very little work over Afghanistan of Iraq and are not usually deployed anymore since we ran over Iraq. They are not needed; we have bases in both of those countries and operate fighters from inside the countries.