Technology and Operations
This forum is for discussing technological & operational matters pertaining to U-boats.
Re: Depth Charges and ASDIC/Sonar
Posted by:
Ken du
()
Date: August 13, 2002 01:22PM
Hi Durand,
In the beginning ASDIC was pretty limited. It had a limited range, could only determine relative bearing to target not depth and could not be used if the boat carrying it was traveling at high speed. Also, it only looked forward as the noise from the props of the boat carrying it interfered with it otherwise. Thermoclines (layers in the ocean where the water temperature changes a great deal) were also a problem. The main tactic used by U-boats against it however was to attack on the surface at night thus rendering ASDIC completely useless.
Also the early depth charges were not powerful enough and sank too slowly. They also could not be set to detonate at anywhere near a U-boat’s maximum depth. Additionally they were launched by rolling them off the stern which meant that were going to detonate behind the boat that dropped them.
Germany knew all of this and U-boat commanders used the information to escape from depth charge attacks by for example changing depth and direction during the attack when the attacker was blind.
As the war progressed allied radar, control of the air and other innovations forced the U-boats to submerge more of the time and rendered the night surface attack less of an option. ASDIC improved and could eventually determine the depth of the target. This was coupled with a launcher that could set the depth to detonate its depth charges from the ASDIC information, however the sinking rate of a depth charge was known and when the U-boat heard them hit the water they could still change depth and direction. The sinking rate and the maximum depth was later improved too. The real breakthrough was probably the hedgehog. It didn’t detonate until it hit the U-boat and thus allowed the ASDIC operator to continue to track the U-boat during the attack. Since it had a smaller charge (still effective because it was close to the U-boat when it detonated) the noise and other disturbances from the detonation were less too. Additionally they could be launched from the bow of the attacker.
Germany developed counter measures like Bold (a device that generated bubbles which were able to fool ASDIC) that were effective for a time. The acoustic torpedo can be considered a countermeasure since it was planned to use it to sink the attacker on his run in.
Developments like FIDO (air launched acoustic homing torpedo) helped seal the U-boat’s fate. Once the U-boat dived the FIDO could be dropped in its swell and would home in on the U-boat’s props while it was trying to get away. Since the U-boat was running flat out trying to escape and since FIDO was dropped after the U-boat was submerged, the U-boat wasn’t even able to tell they were being attacked by a FIDO.
In summary, at the beginning of the war the U-boat had little to fear from ASDIC and depth charges but this changed over the course of the war until it turned almost completely around.
I don’t have a specific source for the above. I have read pieces of it in different books and it has been discussed here on the forum in the past.
Regards,
Ken Dunn
In the beginning ASDIC was pretty limited. It had a limited range, could only determine relative bearing to target not depth and could not be used if the boat carrying it was traveling at high speed. Also, it only looked forward as the noise from the props of the boat carrying it interfered with it otherwise. Thermoclines (layers in the ocean where the water temperature changes a great deal) were also a problem. The main tactic used by U-boats against it however was to attack on the surface at night thus rendering ASDIC completely useless.
Also the early depth charges were not powerful enough and sank too slowly. They also could not be set to detonate at anywhere near a U-boat’s maximum depth. Additionally they were launched by rolling them off the stern which meant that were going to detonate behind the boat that dropped them.
Germany knew all of this and U-boat commanders used the information to escape from depth charge attacks by for example changing depth and direction during the attack when the attacker was blind.
As the war progressed allied radar, control of the air and other innovations forced the U-boats to submerge more of the time and rendered the night surface attack less of an option. ASDIC improved and could eventually determine the depth of the target. This was coupled with a launcher that could set the depth to detonate its depth charges from the ASDIC information, however the sinking rate of a depth charge was known and when the U-boat heard them hit the water they could still change depth and direction. The sinking rate and the maximum depth was later improved too. The real breakthrough was probably the hedgehog. It didn’t detonate until it hit the U-boat and thus allowed the ASDIC operator to continue to track the U-boat during the attack. Since it had a smaller charge (still effective because it was close to the U-boat when it detonated) the noise and other disturbances from the detonation were less too. Additionally they could be launched from the bow of the attacker.
Germany developed counter measures like Bold (a device that generated bubbles which were able to fool ASDIC) that were effective for a time. The acoustic torpedo can be considered a countermeasure since it was planned to use it to sink the attacker on his run in.
Developments like FIDO (air launched acoustic homing torpedo) helped seal the U-boat’s fate. Once the U-boat dived the FIDO could be dropped in its swell and would home in on the U-boat’s props while it was trying to get away. Since the U-boat was running flat out trying to escape and since FIDO was dropped after the U-boat was submerged, the U-boat wasn’t even able to tell they were being attacked by a FIDO.
In summary, at the beginning of the war the U-boat had little to fear from ASDIC and depth charges but this changed over the course of the war until it turned almost completely around.
I don’t have a specific source for the above. I have read pieces of it in different books and it has been discussed here on the forum in the past.
Regards,
Ken Dunn
