The floor plate looks like it may have been etched for depth and rough-out. Then additional detail added with gravers.

I think the initials are 'L W T W, Jr'

Maybe just 'L W T Jr' with an extra fancy T to hang Jr on.

Maybe 'Lt. W W Jr.' w/ it's USMC insignia

Hard to put multiple letters in order sometimes. They don't always read straight across or up and down.