MARK SYSTEM / MODIFICATION MARKS

All equipment, when modified, is normally identified with an indication mark of some sort.

The GPO did just this but there is no specific instruction explaining how to mark equipment or the dates when different marking systems were introduced.

Below is an explanation of the GPO system, but there is no guarantee of accuracy for the statements made.

An early form of marking the modification status was a three digit code.  The first code was Mark 234 which in effect was the Mark 1.  Mark 2 would be Mark 235, Mark 3 was Mark 236 etc.

The middle digit should also have some significance, but that is a mystery.

The earliest found three digit code is 1913.

Around 1934 the system changed to a simple Mark 1 or Mk 1, but the original, three digit system, still continued into the late 1930's sometimes overlapping with the new.

Last revised: December 20, 2023