[Olamagato]

Originally Posted by PapaKilo

Correct me if I'm wrong, but aren't destroyers capable to drop DC on you, even when they can't ping you, cuz the boat is actually under the active sonar beam in SH3 ?

Submerged submarine to be detected in two ways:
1: He could generate noise (motion of ship propellers in the water, the sounds coming from the ship). It can detect both simple hydrophone or more sophisticated passive sonar (using hydrophone arrays).
2: He could not generate any noise (for example, could be completely stopped and no one on board seemed no sound), but if his body was hit by a beam active sonar, it became immediately detectable by the passive sonar coupled with active sonar (this was in indeed, a complex device).

Even the smaller patrol boats who doesn't even have an ASDIC, except passive sonar, can easily put the barrels on u-boat. Because I think there is no difference much in SH3 between active/passive sonars WHEN they hunting.

Small patrol boats were allowed to have only a hydrophone / sonar passive because they were not easy and profitable target for the U-boat, even standing motionless on the water and scan his presence. Then it did not generate any noise their own, so detection may be quite good.

However, the fast escort ships generate their own, a big noise, and stop by to listen for the U-boat could be deadly for them. Why did it only in the company of others rushing escort vessels.

Passive sonar hydrophones of the Allies were poor - especially when a ship generate its own big noise. However, active sonar sound reflected from the U-boat hull was so strong that even a weak passive sonar very well locate the target (direction and range).

Beam active sonar had no barriers, nor do they limit the distance. The only real determinant of coverage was the possibility of effective separation of the reflected beam from its own generated and open seas noise. In the later years of the war was used as a carrier of sound inaudible ultrasonic wave, which does not produce an escort ship almost all. Therefore, the quality of tracking has become a U-boat mortally dangerous. The more so that the crew did not know that was tracked (no audible ping).

In other words if they can't ping you because you're too deep, they can track your exact position by noise (if you're loud), moreover with deadly accuracy. This is bad, because passive sonar by it's nature can't give the sonar guy on DD the depth or pitch of the u-boat. So the DC attack (in those situations when boat is under active sonar beam), accuracy should not be always 100% as it is now.

The first reason for the loss of the bearing of the sonar, the ship that really accelerated to drop bombs accurately on the expected path of the U-boat was increasing its own noise. The second reason was the fact that, send the beam of active sonar did not include either horizontally or vertically 180 degrees, the front-bottom zone of attacking the ship, but usually consisted of a cone 65 degrees vertically and 90-130 degrees horizontally - depending on the type of sonar. A narrow beam of active sonar was the reason for the escort ships sailed zigzags to track the U-boat and did circles on the detected location.
Passive sonar scanning had a greater angle (theoretically 360 degrees horizontally and about 60 degrees vertically), but its effectiveness during rapid attack, if no other ship did not send the beam, it was low or none (and it was possible to determine a direction only).

This would also add to say first happy times, more happines, before improved ASDIC was introduced to Allied navy, later in war. Allowing to make critical repairs more relaxed, knowing you're under DD sonar beam, and chance that it drops DC right on your boat is more like coincidental, than a fact.

The reason for the weak U-boat detection by sonar (ASDIC) at the beginning of the war was the use of easy-to-noise acoustic wave in the audible range and a narrow beam of active sonar (for example, only 10 degrees vertically). Also, lack of experience escorting ships crews. The ships, which were only passive sonar (or hydrophone) must quickly find themselves over to the attack, but ships with ASDIC not have to do it. They could, slowly sailing, track the U-boat as long as their rate was significantly greater than the speed of the submerged ship.

Best regards.