(the following story credited to and taken from uboat.net)
ASDIC, developed through the work of the
Anti-submarine Detection Investigation Committee , from which its name is derived, was the primary underwater detection device used by Allied escorts throughout the war.
The first versions, crude to say the least, were created near the end of World War One and further developed in the following years by the Royal Navy.
How it works
The ASDIC, known to the Americans as Sonar, was basically a transmitted-receiver sending out a highly directional sound wave through the water. If the sound wave struck a submerged object it was reflected back and picked up by the receiver. The length of the time from transmission until the echo was received was used to measure the range, which was shown as a flickering light on the range scale. By mounting the transmitter head so that it could be directed almost like a searchlight, the bearing of the target could be read from the compass receiver.
read the rest of the article
http://www.uboat.net/allies/technical/asdic.htm
CLICK THIS LINK TO HEAR ASDIC PING - DONT WEAR EARPHONES TOO TIGHT - MAY HURT YOUR EARS.. CHECK YOUR VOLUMN SETTINGS FIRST.
http://home.t-online.de/home/sgaertner/9son1.wav
The following story credited and taken from
http://webhome.idirect.com/~jproc/sari/sarintro.html
From Asdic, the more modern term SONAR was borne, which means SOund NAvigation and Ranging. SONAR is an American term dating from World War II and is now used universally to describe all underwater detection equipment. In the Royal Navy, the term was not formally introduced until 1964. (read the rest of the story here
http://webhome.idirect.com/~jproc/sari/asd_gen.html
A problem with early Asdic's was their limited search ability as the oscillator projected its
cone shaped beam at an angle of 10 degrees from the horizontal. Below the beam of acoustical energy was a considerable amount of dead space that would permit the target to elude Asdic. If the enemy escaped detection, depth charges had to be dropped by estimating the target's position. Wartime experience showed that this dead zone was even larger than envisioned because submarines could dive far deeper than was originally thought possible. As a result, a clever submarine commander could often manoeuvre out of harm's way. Once contact was lost, it was very difficult to re-establish.
A diagram of ten degrees from horizontal....
