Mk vs. M

Why do the military designations for some equipment start with Mk and some with M, such as M16 and Mk19?

Thanks for your help,

I think ‘M’ nominally stands for ‘model’, and ‘Mk’ obviously is ‘mark’. A rifle might be an M16. When it’s modified (e.g., with a forward assist plunger and a different flash hider) is becomes a ‘Mk.II’; only that’s not how the nomenclature works, so it’s the M16A1. More improvements and it becomes the M16A2.

Mk seems to be used a lot by the British (as an example). U.S. aircraft will use an alpha character at the end of their designations. For example, F-4B, F-4E, F-4J. A British aircraft would be Spitfire Mk.I, Spitfire Mk. V, Spitfire Mk. IX, and so on. Or a Porsche will be 911E, 911S, 911SC. An MGB will be called (unofficially) Mk.I, or Mk.III.

But the Mk19 grenade launcher is an American weapon, I believe. Also, even if it weren’t, the DoD gives M designations for foreign-made weapons like the M240 and the M249. IIRC, when they rev something with a Mk designation they will add Mod to the end of it, e.g. Mk19 Mod 0.

Thanks for your help,

In all my years in the Army, I never saw an official explanation of what ‘M’ means.

M is the Army “model” designation. Over the years, it has been applied with a bit of inconsistency to both weapons and vehicles.
Early weapons used a “year” designation–M1903 rifle, M1911 pistol, M1928 submachine gun–while later ones used a number-within-type series, so that there was both an M1 rifle and an M1 carbine during WWII (and a redesigned M1928 became the M1A1), and still later the numbers were simply assigned to all weapons, serially, regardless of type, so that we are now into the mid 200 range.
Vehicles started out with serial numbers within type (as far as I remember), and, again the numbering system was later reset to include all vehicles, beginning with the Abrams tank. Although that may only apply to armored vehicles, because the various incarnations of the humvee all have numbers in the 990-1030 range.

Mk (mark) tends to be Navy nomenclature, (most easily spotted in the designations for artillery and torpedoes. My guess would be that since the Mk19 was originally a Navy weapon, it was simply adopted by the Army under its original name to avoid the sort of confusion that resulted when the Navy and Army would use the same item under different model numbers (most famously among aircraft).

Actually, the highest number for a humvee appears to now be the M1069.