Post by Don PhillipsonPost by Rich RostromPost by newsso in effect, the deeper the sub dived and DC was
set, the more effective it became?
As mentioned before, the further the depth charge
has to sink, the more time the sub has to move
away.
Also, the depth charge has to be set to a particular
detonation depth. If the attacking ship guesses
wrong about the sub's depth, that adds to the
distance between the sub and the exploding DC.
The main tactical limitation was that the sub-chaser
had to (1) proceed on the surface to the place was
the sub was supposed to be (or calculated soon
to reach, (2) drop the depth charges into the water,
(3) wait enough time for the charges to sink to
the depth for explosion set by their hydostatic pistols.
These processes take time, i.e. time for the sub
to manoeuvre, change direction, etc. Even after
the charges explode, it takes yet more time for
the water to settle down well enough for sonar or
other detectors to start working again.
This was why British sub-chasers installed instead
the "Hedgehog" spigot mortar which fired 15 or 20
small contact bombs in a ring ahead of the ship.
The size and spacing of the ring was calculated
so as to bring at least one bomb into contact with
the submarine if any part of the boat intersected
the ring: and one contact bomb was usually enough to
pierce the pressure hull. The bombs that touched
nothing merely sank into the depths without exploding.
This was a further benefit of the Hedgehog that misses
caused no explosions, i.e. the sonar and hydrophone
detectors aboard the sub-chaser continued to work as
normal, and could track the boat's unseen manoeuvres.
As soon as the spigots could be reloaded, the sub-chaser
was ready for another attack. (Reloading depth charges
required setting the depth pistols for each to explode,
and that took time.)
"Operational research" became a discipline trying to solve a
similar problem with reference to air attacks to submarines.
Scientists (Blackett's Circus) discovered that a better choice
had been to set the airborne DC to explode near surface rather
than at 100 feet.
I read that in a Jagjit Singh book.
Great Ideas of Operations Research.
(c)1968
http://en.wikipedia.org/wiki/Jagjit_Singh_(writer)
<<While performing an analysis of the methods used by RAF Coastal
Command to hunt and destroy submarines, one of the analysts
asked what colour the aircraft were. As most of them were from
Bomber Command they were painted black for nighttime
operations. At the suggestion of CC-ORS a test was run to see
if that was the best colour to camouflage the aircraft for
daytime operations in the grey North Atlantic skies. Tests
showed that aircraft painted white were on average not spotted
until they were 20% closer than those painted black. This
change indicated that 30% more submarines would be attacked and
sunk for the same number of sightings.[19]
Other work by the CC-ORS indicated that on average if the
trigger depth of aerial-delivered depth charges (DCs) were
changed from 100 feet to 25 feet, the kill ratios would go up.
The reason was that if a U-boat saw an aircraft only shortly
before it arrived over the target then at 100 feet the charges
would do no damage (because the U-boat wouldn't have had time
to descend as far as 100 feet), and if it saw the aircraft a
long way from the target it had time to alter course under
water so the chances of it being within the 20-foot kill zone
of the charges was small. It was more efficient to attack those
submarines close to the surface when the targets' locations
were better known than to attempt their destruction at greater
depths when their positions could only be guessed. Before the
change of settings from 100 feet to 25 feet, 1% of submerged
U-boats were sunk and 14% damaged. After the change, 7% were
sunk and 11% damaged. (If submarines were caught on the
surface, even if attacked shortly after submerging, the numbers
rose to 11% sunk and 15% damaged). Blackett observed "there can
be few cases where such a great operational gain had been
obtained by such a small and simple change of tactics".[20]>>
http://en.wikipedia.org/wiki/Operations_research
http://en.wikipedia.org/wiki/Patrick_Blackett,_Baron_Blackett
http://www.di.unipi.it/~gallo/Papers/VoceEtica&RO_02.pdf
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H