Kido Butai Carrier Units Tail Markings

[Witold K.]

Hi everybody
I'm looking for explnation of relation between number of aircraft in Japanese Navy carrier unit and their tail markings. For instance: carrier fighter unit consisting of 21 aircraft should have tail markings from 101 to 121, however there are aircraft with markings like 131, 145 150, 154, 155 etc.
B rgds