My Grandfather's Jacket

I have this Jacket that was part of my Grandfathers(Delbert E Arterburn) uniform. I was wondering if anyone could tell me anything about it? As you can see in the pics there is the letter A followed by the numbers 5434 on the inside of the jacket. I assume the A if for Arterburn. But do the numbers have any significance?

 

I did some more searching, And I belive it's a M1943 Army Mackinaw. Can anyone confirm this for me?

 

It sure is a M-1943 Macinav Jacket.

 

Awesome, Thanks for the confirmation. It's hanging in my room, So I see it everyday. But I never really knew anything about it. My uncle(Who fought in Vietnam) has the uniform he's wearing in my avatar. I can remember taking it to school for show and tell. LOL

 

A-5434 is the owner ID code. First letter of surname and last 4 numbers of army serial number. So the complete ID would be Arterburn ****5434. And yes it's a mackinaw.