So, while I was drafting the preceding article about THE FALL OF ARTHUR, I followed a link at the very bottom of the GUARDIAN piece and discovered that by so doing you can see a photo of Tolkien WW I service pistol (a Webley Mark VI revolver).
Here's the link to the article from six years ago*
and here's the online entry for the item itself (in the 'Personal Stories' section):
Given that I imagine the Imperial War Museum has any number of Great War officer's revolvers, I assume Lt. Tolkien's is included because he's now so popular that it's a good draw for the exhibit as a whole (it's possible, of course, that they just like to make extra links like this to bring the war home to modern museum-goers).
In any case, it shows that, like many veterans before him (most famously, Dr. James H. Watson), Tolkien kept his officer's sidearm after the war was over, since the article notes the gun was acquired by the museum from the Tolkien family two years earlier (e.g., 2004, perhaps not incidently the year after Jn Garth's excellent book had made Tolkien's wartime duty more widely known than it had been hithertofore).
At any rate, wanted to share.
*and here's the article from which that link came: