Counter Attack 4 (Source)

Counterattack will work ANY TIME you are holding either a carbine class weapon or a two handed weapon class based weapon since both carbineer and swordsman have counterattack as their defense. So essentially, you could stack the defenses from the defense line of swordsman and carbineer to acheive the cap on defensive modifiers of +125 to counterattack (any points above 125 will not affect your chance to counterattack since the cap is 125)