What will infantry school be like as a prior service SGT from the marines that already has a combat deployment under their belt goin army ?

You are just some dude coming into the Army. When Pat Tillman and Elvis Presley left their blossoming careers behind and joined the Army they were just some dudes as well. No one cares that you had deployments and you'll have Drill Sergeants who have more deployment time and more schools than you so it will help you to check your ego at the door. In Army schools there are only students and instructors. All students are equal in the Army.

If you have to go to Infantry school in the Army then you're 100% just another dude. I'll leave you with one of the best pieces of advice an NCO gave a young, headstrong Ranger Boyd: "Keep your mouth shut and your ears open. If you're in a class it means you have something left to learn."

Sgt (Join to see) Since most of these people a just spouting anecdotal opinions, I’ll answer your question.

You will get slotted into a OSUT class (somewhere from day 0- partially through). The DS will pull you aside and explain their expectations for you, generally you’ll help them with keeping the new privates in line and teaching them the basics.

You will most likely get your own barracks or living space. And you may even get weekend off post passes.

Don’t expect to be in a leadership position, but be prepared to help out whoever is the position with guidance on being a leader.

Spend your time learning the “basics” of the Army (uniform wear, customs and courtesies, basic tactics [TC 3-21.8 is the infantry bible]). These will help you transition to “Army infantry”.

If you have any questions, ask the DS, and they will help you out. Best of luck on your transition.

You are going to the Army. This means you need to learn how the Army does things - which is different to how we do things in the Marine Corps. Hell, if the Marine Corps would take me back I would have to 100% recycle most of my basic training as it is almost 40 years out of date while my MOS training is 25+ years out of date. Does not matter that I am a SSgt or not. Does not matter if I went to Desert Shield/Storm or not.

The Army does things differently. You need to learn it, embrace it and never utter the words "but in the Marines we did it this way". What you do take with you is that inner training, that mental attitude of a Marine to improvise, adapt and overcome. Combine Army training and ways of doing things with Marine COrps toughness and grit and you will be a great Sgt in the Army.

Don’t be that guy. Nobody cares if you have a combat deployment “under your belt”. If you weren’t infantry in the marines, you are going to be treated like any other infantry recruit.

For all intent and purpose you are some dude. They don't know you. Remember your roots and be proud of them but you need to jump in and walk/talk/bark/squat like the Army. Be humble and hold your tongue because you need to focus on learning.

I was like a ping png ball between Marines and Navy training and assignments. My advice, remember where you are at the time, and do the job they tell you. Each service does things differently. Learn their TTP and rock on.

Honestly there’s a few possibilities and only some of them are half decent. You’ll get to 30th AG, they’ll do a determination of how long it’s been since you’ve been out of the service to see if you need to do basic all over again. If you’re Navy or Air Force it won’t matter because you’ll be a Day 0 trainee. Marines and Army are good (sort of). If you were infantry in either branch then you won’t have to do any portion of OSUT/Basic. If you weren’t then you’ll be told you’ll only do the AIT portion. The issue I saw guys run into was that there were few classes accepting inserts for whatever reason and there’s no choice between Rifleman or Mortars. You could spend months at 30th AG waiting for a class to take you in or accept a Day 0 restart and go much sooner. Also you may wait all that time to be told you’ll be starting week 10 but actually be inserted week 3 or whenever basic rifle marksmanship starts.

Assuming you’ve made it into a class under any of the circumstances above. You have a few new possibilities. They may hate prior service guys and treat you just like everyone else. They might like you and house you separately. They might only like NCOs and everyone else will be separated. They might like you, be housed separately and be basically treated as a secondary instructor if that makes sense. It’ll be a mess, good luck.

TL;DR No one is sure, there’s too many variables and luck involved. Just expect to be a Day 0 private.

I have only two rules: Don't Quit and Keep Your Sense of Humor.
For you I would add: Check Your Ego At The Door.

In my career I have seen way to many disagreements between the Army and the Marine Corp. So much so that I had to stop a Marine Sergeant during a friendly basketball game and remind him that we belong to the same country. Experience, no matter how much, is there for an individual to draw on and not have shoved down his throat. A drill sergeant's deployment may not be the same as the Marine's deployment and comparing notes, instead of egos, will make any soldier, whether Marine or Army that much better.

The big thing you will notice is the discipline and Esprit de Corps varies in the Army. While the Corps has it throughout, the Army has levels. Starting with SF, Rangers, Airborne, 10th Mountain Div., to other bases. You will find as an NCO in some of the other bases this to frustrating in appearance, attitude and work ethic.