The Combat Helicopter is an ultimate introduced in the 13.0.0 update.
It appears to be a military helicopter with a front window, two gray airscrews and pair of metal stands.
It guards the fort, attacking enemies with a machine gun and rocket launchers.
At this moment, ultimates like this are not in the game. It is expected that ultimates will be added to the game at some point due to the fact that the player is able to browse them in the clan fort section, and also in the clan storage, which is quite misleading. At the moment, it is unsure if an ultimate will be an ability used once per game, or if it will be constant.