Weird rolls

I notice my IMP infantry roll 1 in defence multiple of time, that crazy. Can someone tell me the how the critical system work.

I think a normal Infantry unit roll twice. A infantry with 6 defence can roll normal(1-6)+ extra roll(0-6). Highest a Infatry can roll is 12 and with lowest is 1. Basically it roll one from 1 to 6 and the second can roll based on additional base on unit critical chance of 5 %, which can give from 1 to 6 in of a Infantry max defence roll but since it's 5% it might not even have a second roll.

You just answered your own question....

My IF cruisers in ww1 rolled 1's consecutively 1,1,1,1,2 vs dread
Its called luck :p