What aircraft designation is used for antisubmarine operations?

The designation "Antisubmarine" refers specifically to aircraft designed and equipped for the purpose of conducting operations against submarines. These aircraft are typically outfitted with specialized sensors, sonobuoys, and other anti-submarine warfare technology that allows them to detect, track, and engage enemy submarines effectively. Examples of such aircraft include the P-8 Poseidon and the P-3 Orion, which are both integral to naval forces in monitoring and engaging submarine threats.

In contrast, options like VTOL/STOL refer to aircraft capable of vertical takeoff and landing or short takeoff and landing, but do not necessarily imply a focus on anti-submarine operations. Prototype generally refers to an initial model created to test a design concept, and research/experimental denotes aircraft used primarily for experimentation or development rather than operational missions. Hence, "Antisubmarine" is the most fitting designation for aircraft specifically utilized in the role of combating submarine threats.