underwater mines approaching scapa

[Platapus]

Originally Posted by karamazovnew

O Didn't they have a maximum depth at which they could raise the perisope without the lens cracking from the pressure?

To prevent lens cracking, I don't think so. In looking at the schematics of the Type VII, the objective lens (end that sticks out of the water) is always exposed to the pressure that is exerted by the depth of the submarine.

Even when it is fully retracted, the objective end is in a protective sheath but still exposed to the water and its pressure. This means that the periscope lens was designed to withstand the pressures that the submarine was designed to withstand.

However, that does not mean that the periscope could be extended at any depth. It is not the lens cracking that would be worrisome but the seals leaking. When the periscope is fully retracted, a special heavy-duty seal is engaged to help protect the smaller seals. When extending the periscope at depth, the many small seals may be subject to a pressure they were not designed for.

So from a seal integrity standpoint, I am sure there was a maximum depth in which the periscope could be safely extended. But not one for the lens cracking.

In looking at the design of the periscopes, I would imagine the submarine would crack before the lens would crack.

As for being able to see underwater through the periscope, that would be dependent on the light available. One could see much better looking up through the water against the light background of the sky (during day of course) than one could see looking in front where the background is banal.

At depths of about 30 meters, it gets pretty dark/murky at times. I seriously doubt you could see a tethered mine far enough to be able to take evasive action.

Now if you were on the side of the good guys (Americans) you might have had access to the OL and OLA special purpose sonars which were designed to find underwater objects such as mines.