Can you wear your Marine unit patch as an Army combat patch if you deployed with the Marines? Policy appears to say no.

The 224th Engineer Battalion out of the Iowa Army National Guard was authorized to wear 1MARDIV and 2MARDIV Marine unit patch as their combat patch. Had to get written approval through the SECDEF.

I wear the 1st Marine Division patch (Guadalcanal). I served under them in Ramadi and have the letter from Army DCS G1 and GEN Mattis allowing those under our UIC to wear it.
Now as to why I wear it when I have 3 other deployments under my belt? My grandfather was in the 1st Marine Division during Guadalcanal and he left us in 1982. So you can see how this simple thing connects me with someone I barely knew in my family.
The other reason? Because I am authorized to. There are other things to worry about.

Edit - Another good reason: The 1st MARDIV was an awesome group of professionals. Yes there were issues but in the end, the guys I worked with were top notch.

Follow up question sort of related: A friend ask me this one, I'm not sure the correct answer and have seen this both ways. If your former Army and you have jump wings, Do you wear them on an Air Force uniform? There is a req that says all Aeronautical badges must be worn but does that cover jump wings?

I have deployed with 2 MAR DIV, 1,2, and 3 MAW. I have the paperwork showing the deployments were for more than 30 days and I was directly attached to those major Commands. I wear them, because I can. Ever wonder why most Soldiers wear the USMC patches they got? Because deep down, they know the Marines are simply better. And yes, I am a Marine(82-91),

Direct Support DIRSUP , inter service assignments You hump the same hills, breath in the thin air, but when awards are due, alas you were not there

First of all you're not a Marine so hell no. Second of all Marines don't wear patches anyways so why would you think it's ok to wear a Marine patch.

I served in the Navy in Vietnam on River Patrol Boats the Navy was assigned to MACV. I was told it was OK to wear MACV patch on my right shoulder of my BDUs and Class As.

Lt. with all due respect Sir there's a few things you need to be corrected on. And if I'm wrong about this please correct me.
1. As a former Marine myself I don't recall ever wearing a patch.
2. Can you tell me how a Marine "turns" into the Army. We enlisted in the Army for various reasons but we'll always be Marines.
3. From your question it sounds like you are a Marine, correct me if I'm wrong. But when did you wear a patch in the Marine Corps? They haven't been worn since WWII. You may have bought 1 at the PX for whatever unit you were with but you probably didn't wear it with your uniform so how in the world can you expect to wear it with a Army Uniform?

Here's my take.

I deployed in support of a division level asset to 4th ID. They sent me out to go support 1st ID. I did more field work with 1st than 4th. I'd want to be authorized both patches.

When I came back, I only was given memorandums to wear CAPOC. So that's what I do.

The Army can say what they will, but once I'm out, CAPOC, Ivy Leaf, and Big Red One are all going in my shadow box. Haters can hate.

Keep in mind, the combat patch Isn't for others. It's for the wearer. Regs specifically state the Soldier can choose not to wear one. Their option.

Generally, Marine combat patches are authorized to Soldiers assigned to Marine commands. Goes back to WWII. As stated in regs. Of course, there is always exceptions to policy.

Someone may need to check me on this part, but Marines who branched over to Army are authorized to wear an earned CAR. I do know that a CAR can only be awarded to Marine and Navy personnel. An Army Soldier, even if serving with Marines in combat, cannot be awarded the CAR