The Booster Bomb is the fifth cannonball in Jacksmith. Like the Repair Bomb, the Booster Bomb is one of the defensive cannonballs. This cannonball increases your soldiers' damage for a little while. It is acquired in Evershade Forest.
The Booster Bomb is always useful, especially when facing a tough enemy. Booster Bomb has the second slowest recharge, so it should be used wisely and appropriately.