It is increasing your chance to hit if you've a missing streak and if you have lost soldiers. And lower the chance of the enemy hitting you if they've already hit you this turn and you have less than 5 soldiers.
So you can (and will) miss 90% shots, it should not happen twice in a row the same turn.
You can see the code in there : https://twitter.com/m1sp/status/697268847187890176
It is increasing your chance to hit if you've a missing streak and if you have lost soldiers. And lower the chance of the enemy hitting you if they've already hit you this turn and you have less than 5 soldiers. So you can (and will) miss 90% shots, it should not happen twice in a row the same turn.