The warships without ATAS include three Delhi-class destroyers (INS Delhi, Mumbai and Mysore); three Brahmaputra class frigates (INS Brahmaputra, Betwa and Beas); six Talwar class frigates; and three Shivalik class frigates (INS Shivalik, Satpura and Sahyadri).
Ten warships are currently being built without ATAS - four Kamorta class corvettes (INS Kamorta, Kadmatt, Kiltan and Kavaratti); and three Kolkata class destroyers (INS Kolkata, Kochi and Chennai)
A serving admiral told Business Standard tersely: "The MoD is endangering warships worth several thousand crore each, and the lives of several hundred crewmen, by blocking the import of ATAS that costs just Rs 50 crore each."
ATAS is especially vital for our neighbourhood. Warships detect underwater objects (like submarines) with sonar - a "ping" of sound emitted into the water that reflects from submarines, just as radar bounces back from aircraft. In our waters, however, that signal often gets lost. Our warm climes cause a sharp "temperature gradient", with warm water on the surface that cools rapidly as one goes deeper. These water layers at different temperatures refract (bend) sonar waves, often deflecting them altogether from the warship's sensors. With the returning sound signal lost, the warship cannot detect the submarine.
To overcome this, an ATAS is towed by the warship with a cable, extending deep below the surface, into the cooler layers where submarines lurk. With the ATAS positioned in the colder water layers, there is no "temperature differential". Even the faintest return signal from a submarine is detected.
PTAS, unlike ATAS, does not actively "ping". It can only detect a submarine that is emitting sound. Since submarines on patrol are deliberately silent, they emit no sound for a PTAS to detect.
While the Arabian Sea offers tricky, shallow-water operating conditions, the Bay of Bengal is much deeper. Thirty kilometres off Karachi, the ocean floor is just 40 metres deep; while five kilometres off Visakhapatnam, the depth is 3,000 metres. The Arabian Sea, therefore, is the playground of small conventional submarines.
Business Standard
