Thanks guys! Literustyfan, ive kept the crystal based on your description. I’ve finally gotten around to finishing this one. Photos attached. Khaki crown and hand made leather Kitchener strap. All best,From your side view, that looks like the original yellow military crystal that Depollier himself developed in late 1917.
He specifically wrote about it in his 1917 pamphlet, "The Watch in the Trenches".
Depolliers are worth far more if this special yellow "military version" crystal is still intact, the civilian version are clear.
The purpose of this special crystal was to lessen the brightness of the radium lume on the battlefield so an enemy sniper could not pick you off from across "no man's land".
Bright lume on a trench watch was an easy target for a skilled sniper.
If you have not removed it already I would leave it installed.