What characterizes a special purpose sonobuoy?

A special purpose sonobuoy is specifically designed for a particular application or mission need, which is why the correct answer is focused on its tailored functionality. Unlike general sonobuoys that can monitor a range of acoustic phenomena, special purpose sonobuoys come equipped with specialized sensors and features adapted for unique tasks, such as anti-submarine warfare or environmental monitoring.

While other characteristics such as lifespan, operational modes, or frequency bands may apply to different sonobuoys or specific models, they do not capture the essence of what distinguishes special purpose sonobuoys. The primary defining trait is their design for targeted operations, enhancing their effectiveness in fulfilling specific objectives in the field.