Help Identifying a Vintage Constellation

Hi there. About a decade ago, my grandfather passed away and I received this watch. It has been sitting in my safe ever since, but I have not been able to find much information on it. Red and gold logo. On the face it shows it is an Omega Constellation. Electronic 300Hz. In very tiny print at the lowest end of the face, I believe it reads "OM Swiss Made OM". Omega symbol on the outside of the clasp and stamped inside as well. The other stamps are "11" encircled, "750" & "398.001" (I think). I assumed the 398.001 was the model, but I really could find nothing about it, if so. Can anyone give me a good idea of what this watch actually is. I was told that grandpa got it as a retirement gift from the U.S. Army. I am uncertain if that is true. Thank you for any help you can give! I appreciate everyone's time.

It looks to be an Omega Constellation reference 198.7264 in 18k solid gold with an integrated bracelet.

Here's an auction with a similar watch: https://catalog.antiquorum.swiss/en/lots/omega-ref-198-7264-electronic-lot-336-152

Wow! That is incredible. Thank you so much for your reply and so quickly! I have been interested for a long time in finding out more about it, but got back on the search today after some reminiscing about grandad. I was pretty excited to stumbled on this awesome forum. I appreciate you taking the time to respond to me.

He retired after 35 years in 1975, so this seems to fit. I went and did a little reading after making my post, to try and remember the details. He actually was in the National Guard between 1947 to 1975 and retired as a Lieutenant Colonel. This was after his time in the Army, which he served from 1938 to 1946. The Army service always stuck out to me, because of the war.

Interesting the point that JimInOz made, that the military takes back gifts. Makes me think maybe it might have been a group gift. It's a very nice gift if that is true!