There have been a few support tickets asking about berserkers' double strength, so here goes. They get their double strength when the defending army has at least twice the provisions of the attacking army. A few screenshots from a test server to demonstrate this.
Case 1) 10 berserkers vs. 119 archers. 60 provisions vs. 119 provisions. Attack power 3000 vs. Defense power 1190.
After modifier we get the losses for the attacker as follows: (((1190*1,0)/(3000*0,86))^1,5)*10=3
Case 2) 10 berserkers vs. 120 archers. 60 provisions vs. 120 provisions. Attack power
6000 vs. Defense power 1200.
After modifier we get the losses for the attacker as follows: (((1200*1,0)/(6000*0,87))^1,5)*10=1
Case 3) 10 berserkers + 10 axe fighters vs. 139 archers. 70 provisions vs. 139 provisions. Attack power 3450 vs. Defense power 1390.
After modifier we get the losses for the attacker as follows: (((1390*1,0)/(3450*0,83))^1,5)*10=3 each
Case 4) 10 berserkers + 10 axe fighters vs. 140 archers. 70 provisions vs. 140 provisions. Attack power
6450 vs. Defense power 1400.
After modifier we get the losses for the attacker as follows: (((1400*1,0)/(6450*0,84))^1,5)*10=1 each
opulation , not propulsion....and bersekers not breweries! 
