As it was explained in the early 1960's to a visiting Soviet Marshal of the Army.
"Sir, you stated that you assumed that we had 17 spires because our capitalist society was unable to raise funds to build the standard 21 spires of capitalist decadence. Sir you are mistaken."
"Yes, Comrade Cadet...so what do you have the 17 spires for?"
"Sir, the spires of are of equal importance to all AF cadets. We have 12 for the holy apostles of the bible."
"Yes Comrade Cadet...religion, the opium of the masses...but who are the other 5 saints represented by the other 5 spires?"
"Sir, the other 5 spires represent the members of the Joint Chiefs of Staff."
I have been around the chapel quite a few times and have never noticed how many it had. I guess I never felt the urge to look up and count them. Makes me feel like an idiot.