If patch is a period one with shirt then worn in Vietnam, then perhaps a member of  Inshore Undersea Warfare Group One.   http://www.iuwg1.stabledoorveterans.com/history.htm

The very first batch of 1219C2s provided to the USMC by anyone was in December 1942 and made by Union Cutlery (Kabar).  These knives had screw-on pommels.  This was per design specs.   After the first batch was delivered to the USMC, it was quickly discovered that the screw-on pommels would loosen up, leading to knife failure. , So the Marines implemented the first "change order".  That change was to weld the pommels tight after assembly.     The first batch of Camillus USN-MK2s (shipped in January 1943/received in February 1943) were 1219C2s stamped USN MK2 rather than USMC.  That is the only difference between a 1219C2 and a USN-MK2.  It's also why I call all USN-MK2s a 1219C2 when typing quickly.   This first Camillus batch was made per the original specs, which included having screw-on pommels.  This batch shipped before the first change order was promulgated/issued.  All subsequent Camillus USN-MK2s  were produced in accordance with whatever specs were in effect at the time of production, as did Union, Pal and Robeson.   The second batch of Union/Kabar 1219C2s had screw-on pommels that were then welded to prevent accidental unscrewing/disassembly.  These can be identified by looking at the pommel face - they have what I call a "round weld scar".   None of the 1219C2s and USN-MK2s made by Robeson or PAL were made with screw-on pommels, to my knowledge.   The second change order basically answered the production question - If we are going to weld the pommel tight, why are we wasting time threading the pommels and tangs?   If we don't thread the pommels and tangs we can make XXX???? more knives per day.   This lead to the change order removing the requirement for the pommels to be threaded on in the first place.  These knives have a "square" or "rectangular" weld scar.   The next two changes were pretty close together - (1) movement of the stamp from the ricasso to the guard in a mistaken belief that the stamp was causing the blades to break at the tang/blade junction.  and (2) reduction in pommel thickness from 3/8" to 1/4".  This change was to reduce the amount of steel being used in the pommels by 33%, not much per knife but literally tons of steel saved over the course of the remainder of the war production.

Here is a controversial Oval attributed to the 503rd. No need to rehash the argument unless it can lead to a definitive answer. Forum members have expressed their opinion as well as several books on the subject of ovals, favoring the 503rd or refuting as such.    

Mark any markings on the otherside? Orientation and placement of SF DOL crest will tell a lot. Although that is the presentation side...It could be a legit sterile early iron guard but the Pak copies also looked similar. But the blade shape does look good. Blade length?

Any help would be awesome!!   Thanks Mark

THIS IS A REPRO CORRECT? I KNOW THEY ARE NOT THE BEST PHOTOS   THANKS mARK

I remember during my deployment another SAW gunner in my company took a round to the 100-round belt bag on his gun (called nutsacks haha).  Here is a image from google. At very minimum it saved his hand!  

Ill be happy to talk to the director and connections I have at my city's military history museum about possibly having it donated and preserved there.  If that's something you'd be interested in, let me know and Ill get in contact with them about it.    Thank you, Hayden

My take on the oval is that it is WWII vintage and US made. I have always considered this one a "generic" as it seems to show up in groupings to soldiers from so many different units. In fact, you will often find this oval glued into patch albums with the title "parachute oval."    I have no issues with this being on a PTO uniform, I would just say that I don't have any experience with it popping up among 503rd groups in any number.   Allan

Looks more like a bullet impact,  but not sure why it didn't go through.   Here's a Pic of some dummy. 50 cal, holes are perfect,  no denting like this one.  Is your bullet a 30.06?