There was a flyover before the Indycar race, which is not a surprise, but the flyover consisted of what appears to me as three civilian transport aircraft. I've seen flyovers with military jets, seen RVs flying in formation, but never transport aircraft before.
The military aircraft *with* guns are probably in the Middle East...
But, the US military does operate a fair number of things that appear to be civilian transport aircraft - That is, they *are* variants of civilian transport category aircraft. I'm assuming you meant large transport jets (of which there are still about 600!) but here's about as complete of a list as I could come up with, totaling 899 aircraft:
Beechcraft/Hawker 400A (127): T-1A Jayhawk (127 USAF)
Boeing 707 (348): E-3B/G Sentry (15 USAF), E-6B Mercury (16 USN), KC-135 Stratotanker (314 USAF), TC-135 Stratolifter (3 USAF)
Boeing 737 (157): C-40A/B/C Clipper (12 USAF, 17 USN, 2 USMC), P-8 Poseidon (126 USN)
Boeing 747 (6) : E-4B Nightwatch (4 USAF), VC-25 "Air Force One" (2 USAF)
Boeing 757 (10): C-32A/B (10 USAF)
Boeing 767 (77): KC-46 Pegasus (77 USAF)
Bombardier Challenger 600 (3): C-143B (3 USAF)
Bombardier Challenger 650 (2): Artemis ISTAR (2 US Army)
Bombardier Global 6000 (11): E-11A (7+4 USAF)
Bombardier Global 6500 (3): ME-11B (3 USAF)
CASA CN-235 (23) : HC-144A/B Ocean Sentry (18 USCG), (5 USAF)
Cessna C560 Citation (38): UC-35B (28 US Army), UC-35D (10 USMC)
de Havilland Dash 7 (3): EO-5C (3 US Army)
de Havilland Dash 8 (16): C-147A (1 US Army), E-9A Widget (2 USAF), P-9 Pale Ale (4 USAF), RO-6A (9 US Army)
Dornier 328 (20): C146A Wolfhound (20 USAF)
Gulfstream IV (3): C-20G Grey Ghost (1 USMC), NC-20G Grey Ghost (1 USN), VC-20F (1 US Army)
Gulfstream V (15): C-37A (12 USAF, 2 USCG, 1 USN)
Gulfstream G550 (9): C-37B (1 USAF, 1 USCG, 3 USN), EA-37B Compass (3 USAF), NC-37B (1 USN)
IAI Astra/Gulfstream G100 (2): C-38A Courier (2 USN)
Learjet 35A (19): C-21A (19 USAF)
Lockheed Electra (7): P-3C Orion (7 USN)