When going officer, can someone from one branch go officer to another branch?

Once you complete your enlistment, you can apply for ROTC in any branch or if you have your degree OTS/OCS.

Once you commission its harder to swap, unless you have a like careerfeild. I have heard that Intel officers have a better chance than say a Army Infantry Officer wanting to be a Navy SWO. Needs of the services and whether there is a plus up or draw down have an effect as well. The Army had a program 10 years ago called blue to green where they allowed AF officers to transfer. I know two that commissioned with me transferred in the Army.

There are a lot of restrictions, but it can be done. My experiences with it were guys who specifically followed the army warrant flight path, or the only other I knew a student of mine in Charleston who left the army to go navy. He was a special case, someone attempted to change the years on his contract while he was in school so he had an opening to apply to all branches to retain his schooling and was able to select a new job. In the end I think he only got accepted to transition because he was eligible for nuclear power and they are significantly undermanned.

Blue - Green program works for E5 Navy to CWO2 Army if im not mistaken