Scopes and pressure

[gordonmull]

This has been bugging me for a while.

When I'm up on the bridge I can see my scopes' heads. What stops them from being destroyed at 150m and leaking water into the control room? Surely a tube made of metal with a glass lens must be extremely vulnerable to pressure.

Also could a scope be raised, say at 60m, without causing damage?

Probably missing the completley obvious. Cheers folks.

[Torplexed]

The periscope heads were small and very sturdily constructed. I know this forum is devoted to U-Boats but here is an excerpt from the US fleet boat manual...

The area of the head window is as small as practicable. Its bezel frame is secured by screws. These screws are of noncorrosive material. The head window and its bezel frame are of sufficient strength to withstand an internal 150 psi hydraulic test or an external 300 psi hydraulic test.

In order to be sure that the head window does not crack as a result of the temperatures to which the instrument is subjected in service, the upper 2 feet of the instrument are tested by being immersed in water and heated to a temperature of 150 degrees F. This temperature is maintained for at least one-half hour. The upper 2 feet of the instrument are then plunged into water of a temperature not more than 70 degrees F and allowed to remain for at least one-half hour. This test is made after the final installation of the head window, but before the optics are in place. Any further adjustment of the head window necessitates a repetition of this test after such adjustment has been made. In Type II periscopes in which a joint between the head and the taper section must be broken when installing optics in the head, this test may be made upon the head only.

In view of the shocks to which this part of the periscope may be subjected in service, such as a depth-charge attack, an ample margin of strength beyond that necessary to withstand the specified test is most desirable. This is especially true of the head window itself.

http://www.maritime.org/fleetsub/pscope/chap4a.htm#4A

That's not to say they couldn't get damaged in a depth charge attack and then the periscope tube floods. That did happen more than once. But they were pretty throughly designed and tested in peacetime in both nations.