David wrote:

What is the history and meaning behind the work "MARK" to designate military
equipment ? The web site www.designation-systems.net says the Navy uses
the Mark - Mod nomenclature but doesn't say what the significance or meaning
of the word "Mark" is. Does anybody know ?

I've only seen one such designation, on a weapon - and it passed
out of our on-base inventory sometime in the late 1970s:
the MK 1 Mod 0 Walleye TV-guided glide bomb, sometimes referred
to as the AGM-62. Think of a big Maverick (AGM-65) missile but
with a bigger warhead and RAT generator instead of the rocket motor.
The Maverick used nearly the same video specs as the earlier
Walleye.