Which of the following are classified as special purpose buoys?

The classification of special purpose buoys includes types that are specifically designed for particular operational needs or missions beyond standard navigation aid purposes. The correct answer identifies BT (which stands for Weather and Environmental Data Collection), SARm (Search and Rescue Monitor), and air transportable communication types as special purpose buoys.

These buoys serve essential roles: BT buoys collect atmospheric and oceanographic data vital for meteorological and environmental research; SARm buoys significantly enhance search and rescue operations by providing location and telemetry data; and the air transportable communication types are designed specifically to facilitate communication in various maritime operations.

In contrast, the other options, while they describe buoys that are used for certain navy operations or surveillance, do not encompass the broader purpose-oriented aspects of the buoy types specified in the correct option. Active listening and passive monitoring buoys are specialized for underwater acoustics but do not imply a versatile utility across multiple naval operations, surveillance and reconnaissance buoys are focused on intelligence and observation missions, and high-frequency and low-frequency buoys relate specifically to communication and monitoring at certain frequency ranges, not a variety of purposes.