Michael, now that is a gold mine of info you have provided, really appreciate that.
On seeing the photo of the two carriers, the first one has a tactical marking within which is
M5. The numbering does seem to indicate M represents the 3rd platoon, while 5 represents the fifth vehicle as set out in this document:
http://heritage.canadiana.ca/view/oo...88/536?r=0&s=5
So far so good, as the CanadianSoldiers site also illustrate the 3" carrier mortar being the no.3 platoon:
https://www.canadiansoldiers.com/tac...ybattalion.htm
What's throwing me is the tactical marking in the photo is in the shape of a HQ unit. So essentially the support company is an HQ unit (with it's own HQ) found within the Company HQ of the battalion.
regards,
Jack