OT Active Sonar and Das Boot

This isnt BF but I recall a discussion a while ago where someone asked
why in Das Boot they went silent when active sonar sould detect them.
Someone answered the question for me so Im pasting it here as its
quite interesting.

The active sonar of that era had severe limitations in range and
direction. Generally they worked for a few hundred metres (500 - 1500
metres - info this site - depending on conditions) directly ahead of
the destroyer. Basically, it was to be used to get an exact fix on a
sub that you had already detected, either visually (periscope, or just
submerged) or through passive sonar.

And active sonar had a blind spot - close to and under the destroyer.
So as the destroyer went in to run over the sub and drop depth
charges, it would loose contact as it got close - and the sub was sure
to try some violent manuever to go where the destroyer didn't think it
would go.

Passive sonar, on the other hand, has a range measured in miles
against noisy targets - like a sub going fast and not trying to be
quiet. But if a sub creeped along very slowly, and the crew shut down
all the machinery, and were very quiet, then a sub was very hard to
detect by passive sonar, even if you were literally right on top of
them. Unusual water characteristics, usually due to temperature or
salinity gradients, could bend sound paths and make both types of
sonar even more problematic.

If you were detected, usually the best thing was to creep slowly and
silently to a different location, direction, and depth then the enemy
thought you had gone to. If you were silent and lucky enough, soon he
would have no idea where you were and you could creep away. But if you
put the pedal to the metal, then everyone could hear you and know
where you were, and then you were a goner: A submerged WWII sub could
not outrun even the smallest surface ASW vessels.

Now, if the destroyer was almost on top of you, charging down on top
of your sighted periscope, or because he had you 'nailed' on active
sonar, yes, high speed, violent maneuvers were called for.

mostly harmless wrote:
> This isnt BF but I recall a discussion a while ago where someone asked
> why in Das Boot they went silent when active sonar sould detect them.
> Someone answered the question for me so Im pasting it here as its
> quite interesting.
>
> The active sonar of that era had severe limitations in range and
> direction. Generally they worked for a few hundred metres (500 - 1500
> metres - info this site - depending on conditions) directly ahead of
> the destroyer. Basically, it was to be used to get an exact fix on a
> sub that you had already detected, either visually (periscope, or just
> submerged) or through passive sonar.
>
> And active sonar had a blind spot - close to and under the destroyer.
> So as the destroyer went in to run over the sub and drop depth
> charges, it would loose contact as it got close - and the sub was sure
> to try some violent manuever to go where the destroyer didn't think it
> would go.
>
> Passive sonar, on the other hand, has a range measured in miles
> against noisy targets - like a sub going fast and not trying to be
> quiet. But if a sub creeped along very slowly, and the crew shut down
> all the machinery, and were very quiet, then a sub was very hard to
> detect by passive sonar, even if you were literally right on top of
> them. Unusual water characteristics, usually due to temperature or
> salinity gradients, could bend sound paths and make both types of
> sonar even more problematic.
>
> If you were detected, usually the best thing was to creep slowly and
> silently to a different location, direction, and depth then the enemy
> thought you had gone to. If you were silent and lucky enough, soon he
> would have no idea where you were and you could creep away. But if you
> put the pedal to the metal, then everyone could hear you and know
> where you were, and then you were a goner: A submerged WWII sub could
> not outrun even the smallest surface ASW vessels.
>
> Now, if the destroyer was almost on top of you, charging down on top
> of your sighted periscope, or because he had you 'nailed' on active
> sonar, yes, high speed, violent maneuvers were called for.

Pretty cool! Thanks

--
[AGB] Creamy Goodness

"220, 221, whatever it takes"