Mar 8, 2015


Sonar - SOund, NAvigation and Ranging
The word Sonar is an American term first used in World War II, it is an acronym for SOund, NAvigation and Ranging. The British also call Sonar, ASDICS, which stands for Anti-Submarine Detection Investigation Committee. Later developments of Sonar included the echo sounder, or depth detector, rapid-scanning Sonar, side-scan Sonar, and WPESS (within-pulseectronic-sector-scanning) Sonar.
United States submarines began using sonar toward the end of WW2 to navigate through Japanese minefields. Ned Beach, upon taking command of USS Piper (SS-409), had his first war patrol as skipper of that boat delayed while a sonar device for detecting and avoiding underwater mines was being installed. As a result, he and his submarine only reached Japanese waters, after negotiating through an underwater minefield submerged, just as the war ended.


Radio Operations Aboard US  Submarines
By Robert E. Straub
     Submarines were equipped with both active and passive sonar gear. The QC/JK gear was located in the Conning Tower. These were companion units with the QC gear being the active and passive sonar and the JK gear was the passive sonar only. Both sonars were manned when the submarine was submerged. A large bearing indicator, for both the QC and JK sonars, indicated the relative position to the submarine's bow of the sound head bearing. The QC sonar had the "pinging" capability, but was rarely, if ever, used due to compromising the submarine's position. The sound heads were raised. lowered and trained from the operating positions in the Conning Tower. The raising and lowering was done by a hydraulic system and the training was done by an electric motor controlled by a handle at the operating station for both the QC and JK sonars. The lowering and raising mechanism for the two sound heads was located at the after end of the forward torpedo room. This allowed the sound heads to be raised inside a protective well when the submarine was on the surface.
    The QC sonar was equipped with a straight key and CW could be used for emergency or identifying purposes.
     Normally headphones were worn by the sonar operators. However, speakers were available. 

     The Fathometer, located in the Control Room, was used to measure the depth of the water from the submarine's keel to the ocean floor. A "ping" would be sent out and the time delay in receiving the return echo would establish the depth of the water. Again, for security and safety purposes this was rarely used. I know of only one occasion that a single "ping" was used for measuring the depth of the water. 

     The JP Sonar gear, passive only, was located in the Forward Torpedo Room and its associated hydrophone was located directly overhead on the main deck. The hydrophone was coupled to the unit by means of a shaft, gear and a crank handle.
    Rotation of the hydrophone was strictly by man power. With the hydrophone being located topside it allowed the submarine to "hear" when sitting on the ocean floor.
    The sonar operators were trained to fire a special acoustic torpedo with this JP gear.
     Late during WWII the JP sonar was replaced with the JT version. This used a larger hydrophone and the training mechanism was improved from the manual operation to a electrical/hydraulic system.
     NOTE: I'm not sure of the designers of this sonar equipment, but I do believe that it was the Underwater Lab at New London, which I also believe has changed its name.
In World War II, the Americans used the term SONAR for their systems, coined as the equivalent of RADAR. RADAR was considered very glamorous and effective, and they wanted to cash in on the name. To be literal they should have named it SODAR (Sound Detection and Ranging) to be the equivalent of, standardization of signals led to the dropping of ASDIC in favor of SONAR for all NATO countries.

There are two major kinds of sonar, active and passive.
Active sonar creates a pulse of sound, often called a "ping", and then listens for reflections of the pulse. The pulse may be at constant frequency or a chirp of changing frequency. If a chirp, the receiver correlates the frequency of the reflections to the known chirp. The resultant processing gain allows the receiver to derive the same information as if a much shorter pulse of the same total power were emitted. In general, long-distance active sonars use lower frequencies. The lowest have a bass "BAH-WONG" sound. To measure the distance to an object, one measures the time from emission of a pulse to reception.
Passive sonars listen without transmitting. They are usually military (although a few are scientific). Passive sonar systems usually have large sonic databases. A computer system frequently uses these databases to identify classes of ships, actions (i.e. the speed of a ship, or the type of weapon released), and even particular ships.

Definitions relating to sound and sonar gear
Absorption. The loss of energy by a sound wave when it strikes an obstacle which does not reflect it completely.
Alternating current (A C). Electric current which flows first in one direction and then in the other.
Amplifier. A device which builds up a weak electric current into a stronger one.
Amplitude. The maximum extent of a vibrating movement. With sound, the greater the amplitude, the louder the sound.
Attenuation. The weakening of a sound wave as it travels, caused by losses due to friction, absorption, and scattering.
Audio frequency. Another-term for sonic frequency; that is, below 15,000 cycles per second. Compare Radio frequency.
Audio-frequency-amplifier. An amplifier for use with alternating currents of frequencies less than 15,000 cycles per second.
Background noise. Noise that tends to mask the sounds you want to hear. Chiefly water noise and noise from the receiver itself.
Band filter. An audio filter which suppresses all frequencies except those between a given high and low limit. For example, the band filter on the WCA gear suppresses all frequencies below 600 cycles and above 1,000 cycles.
Beam. A cone of sound waves, such as is used in echo-ranging. Normally, a beam can be obtained only by using supersonic frequencies.
Beat frequency. The frequency obtained by mixing two different frequencies. For example, by mixing 60,800 and 60,000 cycles, we obtain a beat frequency equal to their difference of 800 cycles. This is called heterodyning.
Cavitation. The formation of a series of vacuums when propellers are turning so rapidly that the water does not flow in immediately as the blade passes through. Propeller noise is greatly increased when cavitation occurs.
Compression. The part of a sound wave where the particles are packed together more closely than normal.
Cycle. A complete sound wave compression-plus-rarefaction.
Decibel. A unit of measurement of intensity of sounds.
Detector. Generally, anything that enables sound to be heard; e.g. the ear. Specifically, in the receiver-amplifier, the detector mixes two supersonic frequencies to give a frequency that can be heard. Also called a "mixer."
Diffraction. The tendency of sound waves to bend around an obstacle in their path and meet somewhere beyond. This accounts for your being able to hear sounds around a corner. (Do not confuse with "refraction.")
Direct current (DC). Electric current that flows continuously in the same direction. A storage battery gives direct current.
Driver. An electrical device used to send a burst of supersonic sound (ping) into the water by means of the projector. In the WCA gear, there are a QB and a QC driver.
Frequency. Number of cycles per second.
Gyrocompass repeater. A device which repeats the movement of the master gyrocompass. The inner dial on the bearing indicator is a gyrocompass repeater dial. The main gyrocompass on a submarine is in the control room.
Heterodyning. The mixing of two frequencies to obtain the beat frequency, which is the difference between them.
Homogeneous water. Water in which the temperature does not change with depth.
Hydrophone. Any device for picking up sound waves from water. It is called a projector only when it also sends sounds out into the water.
Intermediate frequency (IF). The frequency into which the energy entering the superheterodyne receiver is converted in the intermediate stage. In WCA gear, this is 60 kilocycles.
Isothermal. Uniform in temperature. Homogeneous water is isothermal.
Kilocycle (kc). One thousand cycles.
Magnetostriction. Change in size of a metal tube when subjected to an electric current. This principle is used in the JP hydrophone and in the QC and NM projectors.
Modulator. A device which causes a sound to change in pitch continuously. Sometimes used by surface ships in echo-ranging, when an echo is difficult to distinguish.
Negative thermal gradient. Decrease in temperature of water with depth.
Noise level. The volume of background noise heard in the headphones or on the loudspeaker.
Oscillator. A device that produces an alternating current at a particular frequency.
Piezoelectric effect. The development of an electric current when a Rochelle salt crystal changes in size. This principle is used in JK and QB projectors. Compare Magnetostriction.
Positive thermal gradient. Increase in temperature of water with depth.
Projector. The hydrophone portion of QC, QB, and NM gear. Although called a "projector," in submarines it is principally used to pick up sounds. In echo-ranging, it projects the ping into the water.
Quick beating. Bearing of the maximum loudness in sweeping across the target. Also called "Maximum bearing."
Radio frequency. Frequency above 15,000 cycles per second, Compare Audio frequency. Radio-frequency amplifier. An amplifier for use with alternating currents of frequencies higher than 15,000 per second.
Range rate. The rate in knots at which a target's range is changing. Useful in determining the speed of the target.
Rarefaction. The part of a sound wave where the particles are thinned out to less than normal density.
Resonance. The tendency of an object or an electrical circuit to respond well to a particular frequency, but poorly to other frequencies.
Reverberations. The multiple echoes reflected from the surface, bottom, and many small irregularities in the water. In echo ranging, distinguished from the echo, which comes from the target.
Salinity. The saltiness of water. Normal salinity of sea water is 35 parts of salt per thousand.
Scattering. The loss of energy by a sound wave caused by its striking such irregularities in the water as seaweed, fish, and en trapped air bubbles.
Screen. The antisubmarine escort craft which are protecting a convoy.
Sonic frequencies. Frequencies less than 15,000 cycles per second.
Sound shadow. The region beyond an obstruction where a sound is not heard. See Diffraction.
Split bearing. A bearing obtained by computing the middle point between where the signal comes in and where it goes out in sweeping across the target. Split bearings are used only when quick bearing cannot be obtained.
Sweeping. Turning the projector or hydrophone so that it goes through the entire arc of the target's propeller sounds.
TDC. The Torpedo Data Computer-a device in the conning tower which figures out the correct firing data, using the facts of bearings, ranges, course, and speed.
Transducer. The technical term for what is generally called a "projector." A transducer operates both as a hydrophone (picking up sound vibrations and converting them into electric current pulses) - and as a projector (transforming electric current pulses into sound vibrations and projecting them into the water).
Vibration. A continuous back - and - forth movement, producing sound waves in the medium.
Wake. The ribbon of churned-up water astern of a moving ship or submarine. It consists of small currents, eddies and entrapped air bubbles.
Wave length. The distance from a given point on one compression to the corresponding point of the next compression of a sound wave. 

 The Fleet Type Submarine Online
Submarine Sonar Operator's Manual