Alright, this looks like an interesting story even though I'm a little bit concerned with the execution and portrayal.

I'll start by discussing the title. Let me offer some alternatives since you establish yourself that you're not satisfied with it. You want to go with the Air Force-Marine angle.

"Ground and Sky", "Earth and Air", "Hawk and Groundhog", "Joint Training", "Land and Sky", etc. The motif is a bit on the nose but if you want to discuss other unorthodox possibilities, I'm open to it. I got some ideas.

I'm not sure if making John's parents military officers was a good idea because of a lack of reference to a known military history in John's background, even with analysis by Halsey in any of the Halo media though I do think its a cool and splendid idea. I just question the canon-probability of it. No biggje.

From reading the first chapter, what really stands out to me is this feeling of a lack of research into the life of military cadets in military academies and ROTC or whatever officer training program you have in mind. Given Nylund's influence, however, on the mythos, its most likely inspired on the American training model as is much of the UNSC. I highly recommend you do some more research on it, if you like, I did do some ROTC training not too long ago and I have some officer friends who I'm sure wouldn't mind passing on some ideas if you want some pointers.

What immediately stood out to me was referring to the school locales as military basis, while yes, military schools can exist on grounds owned by the government for purposes of defense and security, they are still institutions of learning and should be referred to as such. Call them what they are, military cadet academies. I would look up Corbulo Academy of Military Science in particular since its the only fully-realized cadet academy in the Halo lore as of current. Also, maybe look up actual military academies or junior officer programs for inspiration on what they're like and how they operate. Again, if you need help with it. I'm happy to.

Make sure you're getting the ranks accurate, Airman Basic is an enlisted rank, not an officer or trainee rank. Air Force students should be referred to as "Officer Cadet/Air Force Cadet" and Marine/Navy should be referred to as "Officer Cadet/Midshipman". And make sure to put the individual's last name since shouting it in the middle of a cafeteria without a name will confuse everyone. Cadet such in such will clear up that confusion easily since everyone in training has the same rank with exception to seniority of age.

You can be more creative with your insults you know? Pull some common ones. "Chair Force, Crayon-Eaters, Bullet Sponges, Fob-bits, etc." The world's militaries have great colorful nicknames have plenty of options to chose from, take advantage of it.

I feel like there isn't enough regulation and military conduct being maintained here. Maybe its an attempt to separate schools in terms of style but I feel like this is a bit out there. A basis for regulation should be established across the board to make sure the UNSC is producing quality officers no matter where they come from. The air force school seems to fail in that regard given the stealing of a hat scene. They would have been chewed out and disciplined, both the one who lost their hat and the thief if it was real. Probably with push ups or marching drills as punishment. Though I do agree the Air Force would be more loose on its cadets in some manner.

One of my USAF ROTC buddies says the Air Force really likes people that stick to the book so maybe things in your story changed because 500 years is a long time so make it however you like, just have some restraint with the freedom the characters are given.

Wouldn't curfew mean no one is allowed to leave the dorms? i remember you couldn't leave the dorms after curfew in my ROTC in college without a good reason, usually for the gym or the library. May want to rewrite that to before curfew or change it to one of the dorm rooms.

I would have recommended a mention of a rule about no boy-girl pair by themselves in a private room but since that has certainly changed with culture and time as seem at Corbulo in Halo Forward Unto Dawn with Sully's room mate being a girl.

Anyway, I really like this concept but I think it needs some work. If you want some help, I'm happy to. I think this is a seriously cool idea.

On another note, I also recommend you italicize ship names. I'm not sure why in particular but its a common tradition in military fiction.

generations of exterminating those Insurrectionists scum. They're all dead men walking

how does the name "Duke McCain Warden" sound if you want to change the middle name I understand I have a few other middle names that mite fit better like: McCoy, McCage, McCloud, or Rex.
I thought that the Mc in the middle name could be a Warden family tradition for the eldest child just to ad a bit of history to the family, if you want you get rid of the tradition i just thought it would be cool/interesting.
P.S. i don't know if you saw it or not but I sent you this as a pm, I just coped pasted a part of it.

At least one of Johns parents was a spartan 1

Well reclaimer. You've done it again!

I'm loving this story so far. Gwen seems like a very neat character that I'd love to get to know. I was kind of reminded of that scene from top gun where the admiral calls maverick and goose into his office to send them to top gun when the colonel called in Gwen. Not that Gwen is too much like maveric, but she's certainly not so generic as a lot of military characters can end up being. Her interaction with her friends was also quiet poignant, and god I almost cried when she and Lucas kissed. Poor thing. Stuff like that always breaks my heart(way to easily to be good for me XD). It was wonderful and I'm looking forward to seeing John's father.

Also, I can't believe you beat me to the origin story! I'm still working on the one for Linda's parents. Now that this is out though I might just hurry up and try to get it out there.

Go Army, Sink Navy,
Actual

Hello, Lady Relcaimer!

It is I! You're Fanfic has given me an idea which, for some reason, has absolutlry NOTHING to do with yours... Odd I know...

Anyways, as usual, this was quite enjoyable to read and I can't wait for the next chapter for Glass Cage! XD
~ Mr Wiffels