Sono-Flash: Thales New Dual Mode Passive Active Sonobuoy.

By Xavier Vavasseur - Editor in Chief
Thales is working on a new sonobuoy system, the Sono-Flash, that will combine both active and passive modes in a single buoy. This was unveiled to us during a trip to the Thales site of Brest (Brittany, Western France) ahead of the Euronaval show. Sonobuoys are typically deployed by maritime patrol aircraft (MPA) or maritime helicopters for anti-submarine warfare.

Unfortunately, Thales would not let us take pictures of their Sono-Flash mock-up (it won't be on display at Euronaval 2018 either) and will not share images of the buoy. Here is our best attempt at an "artist rendering" of the Sono-Flash based on what was shown to us at the Thales Brest site.

Thales started working (again) on Sonobuoys at the request of the French Navy (Marine Nationale) and the French Defense Procurement Agency (DGA): France has a strategic need to recover industrial and technological sovereignty in the field of sonobuoys. Thales explained that since the 1990ies the Sonobuoys market relies on two players: Ultra Electronics and Spartan. Nowadays, the French Navy considers that it is no longer sustainable to depend on these companies for its own needs. United States' export restriction is another factor which motivated the development of a new, ITAR-free, system. The final reason is the increase in Russian submarine incursions in French waters. According to Thales, there is a pressing strategic need today for France to recover sovereignty in the field of acoustics systems for anti-submarine warfare (ASW).

Thales' Sono-Flash is based on Thales Australia's Barra Sonobuoy System. It is a standardized Type A sonobuoy (roughly 1 meter long and 10 centimeters in diameter). The Sono-Flash is being developed with the support of the French Navy and DGA. It will be available for export.

Range of sonobuoys currently used by the French Navy (on display at Euronaval 2016).

Thales is looking to achieve technological and tactical breakthroughs with this new system: The unique feature of the Sono-Flash is that Thales managed to combined both active and passive capabilities. So far, sonobouys were always mission-specific and limited to one role (active also known as DICASS and passive, known as DIFAR). The Sono-Flash is fitted with a long reception array similar to those found on passive-only sonobuyos, especially the one found on the original Barra sonobuoy: The design of the reception array is based on the Barra's array. Sonobuoys with a single hydrophone have been in use since the end of the Second World War - but with limited effectiveness. Australian defence researchers Alan Butement and Henry d'Assumpcao in 1964 proposed a much more sophisticated sonobuoy consisting of many hydrophones arranged in a horizontal plane. This was given the name BARRA (a word in one of the indigenous Australian languages meaning “listening”). The Sono-Flash however features a high transmission power as well for the active part, meaning that in active mode, it can receive the echoes from submarines (no matter how silent they might be).

Another advantage of using a unique, dual mode, sonobuoy  is the cost. According to Thales, navies switching to the Sono-Flash will be able to reduce their inventory of active and passive sonobouys by a sensible margin.

Sono-Flash users will be able to conduct multistatic ASW, meaning several transmitters and receivers in different locations (and usually deployed from different platforms) to dramatically increase the coverage area that the friendly force is able to search in: The new sonobuoy frequencies were specificaly designed to be compatible with the Flash dipping sonar. It offer several tactical advantages. For exmaple, the Flash sonar can be used for transmission and the Sono-flash for reception, meaning the tracked submarine will know the position of the dipping sonar but will not know the position of the sonobuoy. Several Sono-Flash can even work with each other to ping in specific patterns (or randomly depending on the mission).

Sonobuoy launcher aboard a French Navy ATL2 MPA.

Digital acoustic data is sent from the buoy to the aircraft via VHF radio link for processing. The UHF radio downlink is used to command the Sono-Flash such as to change its depth or reset the transmission codes or retask it from passive to active modes. The endurance of the buoy is eight hours (after which it sinks).

We were told that the Sono-Flash development was very much linked to the Atlantique 2 (ATL2) upgrade programme of the French Navy. Sono-Flash in "Type A" form factor will also be compatible with the VSR700, the future VTOL UAV of the French Navy.

During our visit we were shown a full size mock-up of a deployed Sono-Flash. Thales also has a demonstrator to run some tests (both hardware and software, first in a pool in Brest, then in a lake and finally at sea). Thales started technological operational studies five years ago. The first phase of the detailed design has just been completed following some flight tests (from October 2017 to June 2018) involving ATL2 MPA and NH90 NFH. The next step will be the test of a prototype. Thales expects to be ready for mass production within two to three years.

Old (from the 1970ies) infomercial on the BARRA sonobuoy on which the new Sono-Flash is based (for the passive part)