When a plane is mk I, mk II, etc. what does that mean?

Question

When a plane is mk I, mk II, etc. what does that mean?

Answer 1

It means model number, basically.  Usually some significant change has been made, so the manufacturer renames the aircraft.  For civil aviation, it can also be a sales gimmick not unlike that of cars-"buy the ALL-NEW x*x MkIII!".

Answer 2

version

like the spitfiers... initial production was the mark I, and the post war versions were xxiv

Answer 3

Mark I, Mark II, etc.

Answer 4

You mean Mach... Mach is the measurement of speed of the sound.

Mach 1 = Speed of Sound

Mach 2 = 2x Speed of Sound

If you're flying 78 percent of the speed of sound, it is also referred to as Mach 78.

Answer 5

It just means "version number."  It's chiefly a British tradition, but will be found in any English-speaking culture.

The WW2 Supermarine Spitfire pursuit aircraft was famous for coming out in Mark numbers running 'way up into the teens.  I had a friend who flew a "Spit sixteen," meaning a Spitfire Mk XVI in the war.

One answerer got "Mark" confused with "Mach," and needs to go back and get his brain upgraded to Mk 2.