Which aircraft is primarily used as a training helicopter?

The TH-57 Sea Ranger is primarily used as a training helicopter due to its design and role within the United States Navy's training programs. This aircraft is specifically tailored for training purposes, providing a platform for student pilots to gain essential flight experience and develop their flying skills. The TH-57 offers a suitable and controlled environment for instruction, which includes basic and advanced flight maneuvers.

Other aircraft listed, such as the MH-53E Sea Dragon and SH-60 Seahawk, are utilized primarily for operational roles, including search and rescue, anti-submarine warfare, and vertical replenishment. The V-22 Osprey, a tilt-rotor aircraft, serves different operational capacities, including troop transport and logistical support, rather than dedicated training. Thus, the TH-57 Sea Ranger stands out as the clear choice for training missions.