The helicopter is a plane unit made in the airport. It can garrison up to three troops and fires at the same time. The amount of damage dealt depends on the amount of units garrisoned. It was added in the most recent update.
Mainly in the middle of the game, helicopters can be used to carry some soldiers. It can act like a tank for soldiers and can have its damage enhanced with the soldiers garrisoned in the helicopter. Only three soldiers are allowed to be garrisoned into the helicopter.
If the unit is a sniper, the damage the sniper does will not add on the damage if it is attacking something other than a soldier.
Since the helicopter can enhance its damage with soldiers, it can be used to carry units to not only enhance its damage, but shield the soldiers from harm until is dead/sold. Although, because the helicopter has low health, it should only be used in small attacks and not attacks on a base.
Because the Helicopter is a relatively fast air unit that can garrision infantry, it can be used as a quick way to transport slower infantry such as Juggernauts quickly across both land and water.