The CAPTAS-4 is a towed array sonar developed by Thales Underwater Systems to equip first-rank surface combatants.
Manufactured in Brest, France, it represents the high-end and most powerful system of the company's CAPTAS (Combined Active and Passive Towed Array Sonar) line of products[1] and equips several first-rank warships of the French Navy as well as those of various export customers.
In addition to the UMS-4249 variable depth sonar, a towed multi-functional linear antenna equipped with hydrophones is used to capture radiated noise and reflected signals: it picks up the feedback of Very Low Frequency (VLF) emissions from the UMS-4249 to locate, classify and track a target, while at the same time providing passive detection that only listens when active sonars are not being used.
It is also designed to detect the specific noise of torpedoes, providing an early warning to deploy countermeasures in the event of a submarine attack on the vessel.
[2] The great attribute of the CAPTAS-4, which separates the transmitting and receiving instruments, is its ability to detect submarines at long range (up to 150 km, 93 mi)— allowing the formation of a "safety bubble" around a carrier battle group for example— and instantly determine where the noise is coming from (port or starboard), which is an advantage on the high seas, but also in coastal areas, where the number of signals is very high.