Active duty Marine transfer to Army OCS, with less than 9 years active time. How to apply to Army OCS while on USMC active duty?

You need to talk to your state ocs officer strength manager. They will start your packet and give you the guidance you need. We have a Marine in our ocs unit, it's great to have USMC experience in our training. Very valuable leadership.

Talk to your S1. They should help steer you to the individual that handles OCS for Marines who should in turn steer you to someone that can help with Army OCS and interbranch transfers.

As far as the packet, the most you can do for now is go on the Army HRC website and find the OCS tab. This will take you to a page with all the mandatory paperwork for an OCS packet. This is the bare essentials. So start knocking them out. Eventually you will be told what the additional items you'll need for your packet based on your unit and branch.

I had a couple of peers at OCS who were prior Marines. They had to ETS out of the Marines and then go to an Army recruiter. Once you are close to your ETS date (a few months out), I would recommend completing your OCS and start calling recruiters (find one who is willing to help an OCS applicant) packet in order to submit the day after your ETS.