The invention to seek out enemy subs

28 December 2022

This history article, telling the story behind the development of one of Defence’s most successful joint development projects, is one of a series celebrating 115 years of Defence science and technology.* 

PROJECT: The Barra sonobuoy

Sonobuoys were first developed and used at the end of World War 2 in response to the German U-boats’ destruction of allied merchant ships in the Atlantic.

The ability to locate submarines so they could be sunk, or prevented from attacking, became critical for the Allied war effort, and so the idea of the ‘buoy sonar’ was born.

The idea was simple: a sonobuoy would be dropped into the water by aircraft and, on impact, an underwater acoustic sensor (hydrophone) and floating radio transmitter would deploy. Any signals detected by the hydrophone – caused by a nearby U-boat, for example – would then be relayed to the aircraft via the radio transmitter.

Perfecting a good idea

However, early sonobuoys that consisted of a single, omnidirectional hydrophone were limited in range and effectiveness. In 1964, Alan Butement, the first chief scientist within Australia’s Department of Supply, along with the future chief Defence scientist Henry d’Assumpcao, proposed a more sophisticated concept for a ‘directional’ sonobuoy. Both took out the original patent.

Although the two scientists conceived the idea, its realisation depended on the work of a vast number of engineers.

The Weapons Systems Research Laboratory of the Weapons Research Establishment (which became part of what is now Defence Science and Technology Group) began work on the Barra project, initially known as the Nangana Project, in 1964.

Their task was to develop a sonobuoy system, with multiple hydrophones arranged in a horizontal plane, which could be deployed from the air to locate and classify quiet submarines and surface ships.

A new design

This new Barra sonobuoy consisted of two parts: a surface float and a sub-surface component that separated on impact with the water after being deployed from an aircraft.

The sub-surface component was the sonobuoy launch canister, a 1200mm long tube with a diameter of 120mm, which was ejected out of the maritime patrol aircraft using a small explosive source called a CAD (command activated device).

It deployed a small drogue (parachute) to ensure the buoy entered the water correctly. On entering the water, a saltwater battery was activated, setting in motion the deployment of the horizontal acoustic receiver array to a pre-set depth and the radio-frequency transmitter that floated on the surface.

The acoustic receiver array (originally envisaged as a cruciform array) had five telescopic radial arms that deployed once the buoy was submerged, with five hydrophones on each arm that would pick up relevant data and send it via the surface float to a sonics processor in an aircraft.

Two or more sonobuoys working together would allow for the detection of multiple noise sources and their direction of movement.

This gave the Barra a huge advantage over existing sonobuoys. With so many hydrophones, the incoming signal was amplified by as much as 14 decibels and the processing system could determine the direction of the signal down to a couple of degrees.

A feat of engineering

While the concept was straightforward, the engineering task that followed was not. A detector array of several metres in diameter had to be arranged inside a small canister, along with sophisticated microelectronics that could withstand being dropped from a great height, as well as being immersed in water at sometimes near-freezing temperatures.

In the initial development, an underwater test facility was established in South Australia, and the trials undertaken there led to an improved, more efficient sonobuoy model.

In 1967, sea trials were completed in St Vincent’s Gulf, South Australia and later off Jervis Bay, NSW in close collaboration with the Navy and the Air Force.

Partners in production

The development of the Barra sonobuoy system included the sonobuoy itself, which was designed and manufactured by Australian scientists, as well as a sonics processor – the AQS901 airborne computer. This computer, designed and manufactured in the United Kingdom in accordance with an agreement in 1975, picked up radio signals transmitted from the sonobuoy and processed them.

In 1977, Amalgamated Wireless Australasia Limited was awarded the initial contract to produce Barra sonobuoys. The first production Barra was presented to the United Kingdom’s High Commissioner for Australia in 1980, marking the beginning of deliveries to the United Kingdom and Australian air forces and navies.

Over time, more than 56,000 sonobuoys were manufactured, earning Australia in excess of $200 million in exports.

* Defence science in Australia can be traced back to 1907, when Cecil Napier Hake was appointed Chemical Adviser to the Department of Defence. Today, more than 2000 Defence scientists, engineers, IT specialists and technicians form the Defence Science and Technology Group responsible for providing scientific advice and high-tech solutions for Australia’s Defence and national security agencies.



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