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Anti-submarine hunt

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Detection means
HYDROPHONE - Listening device which allows to detect the presence in the vicinity of a sound source (the engines of a submarine, for example). Its functioning is based in the propagation of sound waves across a liquid. The simplest type allows only to reveal the presence of a submarine; the most perfected types can also indicate the direction of the sound source. A good hydrophonist could indicate with enough accuracy the presence and the distance of the target, whereas the depth was calculated. The hydrophone, as all of the submarine search or detection devices, is not capable of giving 100 percent accurate data, for the propagation of sound waves in the water is not lineal, but altered by diverse factors: salinity, temperature, etc... Besides, the hydrophone detects background noise due to marine causes or another reasons such as fish "voices". Its utilization is also linked to the condition of the submarine having the engines turned on. Otherwise, its validity is null, unless there are noises of another type emitted by the unit. At the end of the war little buoys fitted with an hydrophone and a small transmitter were used, being dropped from aircraft. When a submarine crossed the area saturated with buoys, the transmitters sent the noise captured by the listening hydrophones to the center of anti-submarine hunt, which would immediately send an aircraft to the place.

RADIO-GONIOMETER - Electronic device capable of detecting radio waves and revealing the position of their source. It is like an hydrophone of the air, helped by the fact that, having the submarine to transmit from the surface, the depth factor does not have to be considered. Since the U-Boote made an ample utilization of the radio before entering action, even if only for very brief signals, the utilization of a radio-goniometer allowed to prepare for an imminent attack and, if the emission was long enough, to determine the position of the attacker.

ECHO-GONIOMETER - Denominated ASDIC by the British and Peritero by the Italian, it was devised by the Allied Submarine Detection Investigation Committee, which began the research about this device in 1917. It is a system which takes advantage from the reflections suffered by acoustic waves propagating on a liquid when they hit on an obstacle. The ECG comprises a pulse generator, a projector which irradiates the pulses on the water, and a receiver which receives the pulses which, after having hit on an obstacle, return reflected to the source. This device is subject to all of the inconveniences of the hydrophone in duplicate, for the causes which disturb the reception of the hydrophone in a single way, the submarine-hydrophone path, in this case appear also in the projector-submarine path. The most perfected ECG types were already capable of giving important data about the location and the distance (the depth was calculated) regardless of the position of the submarine. In the phase of approximation, however, the contact was lost at certain distance, and the attack with depth charges was effectuated according to estimated calculations.

RADAR - Electronic search device so called after the initials of the words Radio Detection and Ranging. The functioning of the RADAR is based in the reflection suffered by electromagnetic waves propagating on the air when they hit on an obstacle. Its utilization, naturally directed toward the sky, is analogous to that of the echo-goniometer. Used in the sea for the search of small targets (the conning tower of a submarine), it is a device of difficult utilization, for it is strongly disturbed by the surface of the sea, the waves and other factors, but it can give good results. Its utilization is particularly fearsome for submarines when it is installed in an aircraft, given the swiftness of the attack which follows the detection.

AERIAL SEARCH - Particularly feared by the submarinists, for in the first years of the war the U-Boote were not fitted with aerial detection radars and their anti-aircraft armament was a modest one. The aircraft was capable of quickly watching large extensions of the sea and, in the event of detection, to dive upon the target to bomb it with depth charges even if it was not yet submerged. The later utilization of aircraft combined with radars gave excellent results.
Attack means
ANTI-SUBMARINE CHARGES - Anti-submarine charges are metallic containers which contain explosives (from a dozen of kilograms to up to several hundreds), a detonator and a regulable hydrostatic device which causes the charge to explode at the pre-determined depth. The shape of these charges, which is generally cylindrical, was gradually modified to resemble the silhouette of a water drop, which is much more hydrodynamical and capable of descending through the water with a higher speed to explode as close as possible to the submarine before this one can get away. These charges can be launched from:
Special types of throwers were:
CHUTES, which dropped them to the water on the trail of the ship.

THROWERS, which were similar to catapults or small cannons, in whose muzzle the charge was placed, and which were actuated by either explosive cartridges or compressed air. They were generally arranged sideways on the bridge of the ship, and they launched the charge at some dozens of meters.

HEDGEHOG, a multiple thrower capable of launching at the same time 24 charges which fell to the sea forming an ellipse. When sinking, if one of the charges hit the submarine it exploded, causing the explosion by sympathy of the other 23 and generally destroying the submarine.

SQUID, a thrower similar to the former one, but with only three charges of a greater weight, with a fuze of hydrostatic besides impact effect.

Whatever is shown here is valid, naturally, for warships only. For transport ships, unarmed for this kind of warfare and therefore absolutely defenseless against the "grey wolves", the only possible form of defense was to navigate in convoys to allow the escort units to control the sea around the course set in a more capable way, but ready to disperse themselves in every direction at the first warning of attack.

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