WW1 Regina/Fahys Sterling Silver 15J Trench Watch. OMEGA movement??

I have an all original WW1 Regina trench watch with a Fahys sterling silver case and guard. Movement is marked regina watch co Swiss 15 jewels adjusted 2 positions. The serial # on the movement 4975738. The serial # on the back case cover which reads Fahys Sterling Patent Pending, 10320668. There is also a number on the lip of the main case 81568. I have read Omega purchased Regina around 1915 and it may be an Omega movement with the Regina brand on it. I would appreciate any insight and information on the watch and it's history. Thank you.

Here is just one more photo with the guard attached.

Could be most likely an Omega 17:
http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&168&2uswk&Omega_17LIBN

Just be careful it seems there is lume dust everywhere over the dial and most likely it`s Radium don`t breathe it in.

As a side note the crystal because of it`s yellow colour it is most likely made of zelluloid as most people don`t know they can be polished to a crystal clear state again so no need for a change which is a pity everytime that happens.

Thank you very much for the information on the movement and the crystal. I'm glad to hear that the crystal can be polished without replacement. Thanks

You`re welcome!

The process of polishing is completetley different to plexiglas-crystals you have to use Ethanol/pure Alcohol (spirit) and a sturdish piece of cotton cloth like you use for drying tableware.
Do you know how to proceed?

It would be my first time with the method you described

OK then,
please forgive my bad englisch I`m no native englisch speaker:

You wet the cloth with spirit on one point but not that it is totally wet
Then you press the crystal with medium pressure onto that area and polish with the cloth fast in circles
You will notice a specific smell like campher therefore you know it`s really celluloid
You proceed untill the spirit is gone and furthermore
The resistance while polish will raise go on at the same speed and pressure like before untill it goes smooth
Repeat that until the crystal is completetley clear mostly you need three minutes each round
Mostly you need one round on the inside also

Regarding to it`s age it can be that the crystal will stay a littel yellowish that`s because UV have deep impact on those celluloid crystals but after you`d polish it will stay like that for the next 20 years 👍

After polishing your crystal will be soft instead of resistable thats because celluloid takes water so let it dry after all is done.
Other than plexiglas crystals your celluloid crystal if treatet well can last forever they don`t crack from UV and heat.

Just to think about the fact that yours is like 100 years old!

If it doesn`t work out like I desribed there`s another method with toothpaste but this I don`t recommend because it take a looooong time.

Vintage celluloid is very brittle and there is a small risk of it catching fire. People replace them because after a hundred years, they are unsuitable for the job. Sternkreuz makes a nice replacement crystal.

Just as an example before:

After:

Thank you for information about the crystal and Sternkreuz.

Thanks again you have been more than helpful. I will let you know how it goes. Thanks