If you add up the individual digits of any multiple of 9, you will always end up with 9 or a multiple of 9.
example: 9 x 47= 243. 4+2+3=9
another: 9 x 648= 5832, 5+8+3+2= 18. 18 divided by 2 =9
'Commando' came from soldiers who were too busy to squat in combat so they didn't wear underwear so that their shit went down their pantleg instead of bunched-up in their pants.