If the badge has been on the hat for 80 years it should leave an impression on the hat.   Many people call this ghosting.

The only way you will know for sure if the badge is original is if you have a Time Machine, it is the right style for the hat and that is the best anyone can do. As for the semi-crusher, either it is or it isn't and this one isn't, that is like saying you are semi-pregnant.   

There are so many amphibious units that used the red square, and is not purely limited to usmc. Honestly you might see more army using them than any. My examples here can help shed a little insight to the possibilities. The far left was used by a man in the 96th ID wounded at okinawa. The middle has regimental insignia tracing to the 592nd EBSR of the 2nd engineers. The one on the right bears the earlier double horizontal bars of the 2nd marine engineers seen at tarawa. Repainted with a camo and later seen red square. A friend of mine also has a red square helmet identified to a seabee in the 133rd ncb at iwo. So much more has been found out about these in recent times. But they still leave questions to be asked at the same time.

I would just throw it in the washing machine with a good amount of bleach, it will be dry before it has a chance to rust. That is the way the navy did it and it worked for them. 

Very nice jacket.    

We need to see a picture of the whole scabbard and the bayonet. Before we entered WWI we made P-14 rifles for the British then in 1917 we rechambered them for 30-06 and used them ourselves. We also supplied old M-1917s to Britain under Lend-lease in WWII. So there could be several reasons for the broad arrow including it has been messed with.   

Hello Thank you all for you help and comments Tony

Posts like this are why I LOVE this forum and its contributors!     Thank you for sharing and for your dedicated custody of this treasured item.

I was once told that "AGO" stood for "Approved Government Outfitter" and was used to denote that they were an approved source for insignia etc. GEMSCO used G-2 and G-52 as their Approved Government numbers.   I have no documentation for what I have just written, so you can take it with a grain of salt, but it seems to make sense to me at least.   Allan

Thanks for posting that, jsand. That perfectly illustrates the problem with pewter buckles: they wear to the extreme with major loss of detail.