1940s Eterna Birks military watch

I recently encountered this watch on eBay and was intrigued to see what appears to be a Canadian Regimental number, engraved on the case-back. After consulting Clive Law's book, it seems that the "M" corresponds to Militia District 13, which consisted of the province of Alberta and what is now called the Northwest Territories. The "51543" falls within the block of numbers given to the "85th Fd Bty, RCA". The "RCA" stands for Royal Canadian Artillery, and the "Fd Bty" stands for Field Battery. The Birks-signed dial fits with the Canadian provenance, and the serial number on the movement seems to date the watch to the early 1940s, which fits with the Regimental number.

Someone please save me from myself and purchase this neat watch!

eBay link: https://www.ebay.co.uk/itm/204312060374?hash=item2f91f2a1d6:g:WXUAAOSwzsxkQpH5&amdata=enc:AQAIAAAA4AJf7DpmB2529a5z0DqnnbNtc9RrurfmO9eSCM/ApUCbztsES2ijR5jFrKBYSvKahec7ZHRwirkBqiAGGF1RESXqYmBlXxG+D5+0DXtQ8nmwTZ3i0uqZSTnBiiLAtt0T7IRaBAKvC3RACUBwOtgwpLkEa9VXjBolJJjC+dapCt/NF7MGr+f4N+oGHp5Aw0y+GLKXbL9tvKjtjO7MLCT+vRJ5SqIgJQ/lZ+IrQPZpbqobWfQOGzsMy96xl5/P8EsOO34I3017undWngO3PwX3dFTqAb6foctnslCDgHvqSrCO|tkp:BFBMru_u-Pdh

P.S. Here is a thread I made last year about a 1941 Longines with a Canadian Regimental number: https://omegaforums.net/threads/1941-longines-with-military-connection.150015/

Thank you for checking Ancestry, and for the further recommendations.

I must admit that I was mostly interested in the Regimental number. I did do a quick search for W. F. Humes, but no clear matches came up.

As you guessed, I have spoken with Longines more times than I care to admit.

For posterity, the Eterna sold for 100 GBP on April 28, 2023.