How long is a sub's periscope?

Couldn’t find anything w/ Yahoo. What’s the deal? How deep is “periscope depth”? I always thought it was rather close to the surface, but then read that the sub that sank the Japanese fishing boat came up to periscope depth and looked around before surfacing and striking the smaller vessel.

Periscope depth IS relatively shallow – remember, all of that telescope tube has to fit inside the sub in a straight line. Periscopes don’t “telescope” – they’re packed with optics and electronics, and they have to remain watertight in any case. The periscope in the entrance at Edmund Scientific must be 20-30 feet long (It’s been a while since I visited there).

Modern periscope may be different (there’s no reason you couldn’t just put a TV camera on a stick, I suppose), but I kinda doubt it.

Besides, there’s the old saying, “it’s not the length of the periscope, it’s the motion in the ocean.”


  1. It’s probably different for each submarine.

  2. It’s probably classified for any active submarines.

How big is the submarine? The periscope slides down into the body and typically fits down to about the bottom hull, so it’s height will be the height of the sub, including the superstructure. Minus some overlap. It is pretty shallow, but deep enough that the sub itself is under water.

For a Sturgeon-class boat, about 55’. For a Los Angeles-class boat, about 60’.

The scope usually is projected no more than 10’ above the surface, but by risking broaching the boat, can be raised a bit more.


  1. Yes, PD varies by each class of boat.
  2. PD isn’t particularly secret info. Operational and test depth, that’s classified.

Forgot to be specific: The numbers for boat classes in my previous post refer to Periscope Depth or PD (depth of the keel when at the proper depth to effectively use the 'scope).

BTW: The collision took place after an Emergency Surface drill, which took place some time after the 'scope check.

Yes indeedy. They surfaced, looked around, then went down, and came back up really fast. Remember the jumping-out-of-the-water scene in The Hunt for Red October? That’s basically what they were doing (except not quite that extreme; it’s really hard on the boat structurally)

Not all that hard, but it’s not a good idea to stress-cycle a boat any more than necessary. The usual drill is a partial blow of main ballast tanks from about three hundred feet, not a full blow from >400 feet, which is what you need to create the awesome display usually shown on the tube.

The rest of the issues surrounding the collision are adequately discussed in other SDMB threads.

All you want to know about periscopes & then some: