Each digit can also have a meaning.
For example, in Canada the reserve units are split into regions 1,2,3,4. Each region is then divided into brigade groups. So anything starting with a 3 is Ontario, and the second digit is the area. 31 service battalion is part of 31 brigade, which is in a different area than 32 brigade. So you can have 11, 12, 13 and then the next is 21.
Latest Answers