Submarines and other ships can be tracked either by passively listening to the underwater sound that a ship produces underwater or by listening to echoes of transmitted sound waves that reflect against a submarine (active). The ‘Measurement Building’ started researching underwater acoustics in 1938.
During WWII underwater acoustics was used to detect submarines and surface vessels. Initially, the technique was called ASDIC (Anti-Submarine Detection Investigation Committee); later the term sonar for “SOUND Navigation And Ranging” took off in analogy with “Radar” for Radio Detection And Ranging. Sonar only works much slower than radar because the speed of sound in water is only 1,500 m/s. By comparison, the speed of radio waves is 300,000 km/s. The underwater loudspeaker, also a microphone, which transmits sounds (active sonar) and which captures sounds (passive) and or the echoes (active) is called a transducer.
In 1946, the laboratory reluctantly restarted its underwater acoustics research. Since that time there have been many achievements:
- Post WWII Navy taskings 1946 – 1948
- Active sonar research (ADI, DATO, CWE-1, WARO en CWE-10)
- Passive sonar research (1951-1957)
- Transducer research (1958-1964)
- Doppler shift (from 1957)
- Visualisation of sonar targets (the 60s)
- Sound propagation and the Nereus raft (the 70s)
- Hydrophones: microphones for underwater sound (the 70s)
- Research on towed sonar arrays (the 80s)
- Low-Frequency Active Towed Array Sonar (the 90s)
- SOCRATES (2001+)
- The Waalhaven and HLNMS Paets van Troostwijk
- Former underwater research facilities at Roeleveense Plas, Nootdorp