I was a battalion surgeon in Afghanistan, and a brigade surgeon in an airborne infantry unit, after derm residency. Here’s some advice on how to thrive in the line environment, which I enjoyed thoroughly. I’m assuming you’re O3.
You are no longer a doctor. You are, but really you’re just another staff officer. Also, you’re another dirty captain, most of whom are about to get out of the Army. The BN commander sees you all the same until you prove yourself useful, committed, and humble enough to take instruction. Do not bother or approach the CO until told to do so by the XO, as below.
Find the battalion XO (executive officer, a major) your first day, and ask for time on their calendar. Show them respect and genuine interest in what they want for the unit, and ask how you can help accomplish those goals. Ask for time to figure out how to get there, and for a second date to sit down a month later or so, to go over your progress and any changes in emphasis that need to be made. They may (sometimes) not seem intelligent in the way you’re used to, but they know the army, and can tell you what the unit needs to succeed. Ask for the battle rhythm, what meetings you are expected to be at, and which ones you can benefit from. There’s the bare minimum you should go to, and then there’s the rest of what happens that affects you. “If you aren’t at the table, you’re on the menu.” If you aren’t there when your role comes up, someone will make promises and decisions on your behalf.
Next stop, BN CSM. Ask what the soldiers need to succeed. How can you make that happen, what obstacles have they seen in the way? It’ll usually be something like “the hearing booth won’t see us when we need it”, or “every time someone goes to sick call they get deadlined for a week”. Absorb it, don’t explain or excuse, just sit there and let them vent. Say you’ll do everything you can to fix those issues. Mean it.
Find the battalion PA. Tell them you value their experience and knowledge, and that you’re there to empower and enable them. Use your fund of knowledge when you need to, don’t lord it over the PA as the only element of superiority you have. This person can make your life immensely easier or harder, your choice.
Find your MEDO (usually a 2LT or 1LT MSC officer). This is the person who talks medical to the commander and XO on a regular basis, and who they think is the doctor, not knowing the difference at all, or maybe just not caring. This is the person who sums up your work on a slide, and can be taught what can or cannot happen within realistic timelines. Don’t let them speak for you ignorantly.