perisciope depth and torpedo launch depth on type vii u-boat

[Guest]

What depth was 'periscope depth' for the german type vii u-boat and and at what depth were torpedoes normallly launched?

Thanks for any info.

[hakkikt]

Torpedoes could be launched from

Torpedoes could be launched from depths down to 22 m (limit was the pressure of the air used to launch them from the tubes). Normal torp launch depth was at the surface early in the war and periscope depth later, since visual contact was required (but not indispensable with an experienced sonar operator) to get the data for a firing solution.

IIRC, periscope depth was 14 m (keel).

[JWLaRue]

(but not indispensable with an

(but not indispensable with an experienced sonar operator) to get the data for a firing solution.

This was especially true when the Germans fielded the first acoustic homing torpedoes (T4/Falke and T5/Zaunköning) and the pre-set pattern running torpedoes (FAT and LUT).

-Jeff

[Guest]

interesting info. I've wondered if

interesting info. I've wondered if it would be beneficial to launch the torpedo from just below the surface, rather than at periscope depth. I read that the uboat's periscope was about 5 meters long and that they had a tendancy to vibrate at full extension, due to the force of water rushing by.

It would seem logical to me to submerge to just below the surface, to keep the periscope length as short as possible to minimize this vibration, since fairly precise observations were needed by the captain in order to relay instructions on torpedo settings.

[JWLaRue]

My read of the literature

My read of the literature seems to say that firing at periscope depth was usually done while *not* driving the U-boat at a high underwater speed.

I'd be interested in hearing what others have learned about this question!

-Jeff

[hakkikt]

As I understand the tactical

As I understand the tactical questions, speed, sea state, threat level, and firing depth are interconnected.

The basic requirement is that the periscope has to stand out as little as possible from the surface to avoid being spotted.
If the sea is calm, the periscope is easily spotted, and it makes sense to move slowly (to not cause a wake at the periscope). Depth selection will be more flexible - the boat can come a little closer to the surface and not extend the periscope too much, so that it *just* breaks the surface, and that will cause less vibration.
On the other hand, if there are lots of waves in the water, the periscope is easier to hide - but the boat should be as deep as possible to avoid breaking the surface with the tower.
As I see it, high speed does not make sense in either setting.

I have read that US subs were sometimes driven "hull down", i.e. with only the tower out of the water and using the electric motors, for lower silhouette and faster diving. AFAIK, that was not done with German subs, probably because of their smaller towers.

-Harald

[raalst]

I even think I read

I even think I read somewhere that the periscope could not tolerate full speed extended. the top would be bent out of alignment.

no idea where to find that snippet back, though

[don prince]

Hi Jeff,

Here is some info

Hi Jeff,

Here is some info from a book a "U-boats" by David Miller, and what I found on the internet....

The periscope consisted of a long steel tube which extended out to about five meters from the housing. It had prisms and lenses at both ends, for which there was a switch that allowed the commander to toggle the magnification level – either 1x or 6x. Periscopes suffered from two main problems, the most important was vibration. When fully extended, the long unsupported tube created turbulence on a moving U-boat. At 6 knots, it caused excessive vibration which rendered it almost impossible to use. It was discovered that the frequency of the eddies was the same as the natural resonant frequency of the tube (about 3.2 cycles per second). This was dampened by using an extension bracket to reduce the unsupported length of the tube which increased the natural frequency to 5.8 cycles pre second. The conical tip end was redesigned to minimize the forward hydrodynamic resistance by adding helical wires, which broke up the water flow into general turbulence without any resonating eddies. Nevertheless, vibrations still occurred, but to a much lesser degree. The other problem was fogging of the lenses. Since the damp atmosphere of the U-boat caused fogging, it was especially important that the tube was not only watertight, but was airtight as well. Any fracture on the airtight casing caused by a depth charge attack would result in fogging of the tubes.

Regards,
Don_

PS - I just ordered two of the technical manuals from Germany on the Type VIIc.