Which Sonobuoys are categorized as passive buoys?

Passive sonobuoys are designed to detect sounds in the water without actively emitting signals. This capability allows them to listen for the noise generated by submarines, marine life, and other underwater activities. Among the choices provided, ADAR (Acoustic Data and Report), DIFAR (Directional Frequency Analysis and Recording), and VLAD (Vertical Line Array, Dipole) are indeed classified as passive sonobuoys.

ADAR is utilized for capturing and analyzing acoustic data without actively sending signals, making it a key player in passive acoustic monitoring. DIFAR provides directional data, enhancing the ability to determine the location of sound sources based solely on their acoustic emissions. VLAD, while a bit more specialized, is also designed to collect underwater sounds without transmitting its own signals.

This distinction is vital for effective antisubmarine warfare operations, as passive sonobuoys are often employed to gather intelligence without revealing the listening platform's position. Understanding the functionality of these devices aids in tactical planning and execution in naval operations.