I am looking for the right term for... well, like an air lock on a space station, but for an underwater station. You open the outer hatch, get in, close the hatch, water gets pumped out, you open the inner hatch.

The German word for it would be "Schleuse", but the English "sluice" seems to be limited to the use in waterways (where "Schleuse" would also be correct). "Water lock" seems to be sanitary in nature.

I have this feeling as if I should know the English term, but I really cannot figure it out...

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    it's still airlock...because the aim is to keep the air inside "locked" whatever's outside: void, water or Jello
    – P. O.
    Commented Feb 15, 2018 at 11:20
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    P.O is right. It still remains airlock. You can use 'underwater airlock' or 'floodable airlock'.
    – Kshitij
    Commented Feb 15, 2018 at 11:23
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    It's a good question and on-topic for EL&U. I'd be happy for this question to remain open.
    – Lawrence
    Commented Feb 15, 2018 at 13:48
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    and the term 'lock' comes from the adjustment of water levels in canals. cf. 'lake'
    – AmI
    Commented Feb 15, 2018 at 18:14
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    This isn't the same as an airlock but something you could have underwater but not in space is a Moon Pool aka Wet Porch.
    – Amicable
    Commented Feb 16, 2018 at 15:02

3 Answers 3


The answer is... airlock:

an airtight chamber permitting passage to or from a space, as in a caisson, in which the air is kept under pressure

It's the fact that there is pressurised air inside the "space" that makes it an air lock, not what is outside the "space". "Space" here being a space station, or a submarine, or a plane; and the outside being a vacuum, water, or low pressure air respectively.

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    The OED's first citation is from 1840; "a l is an air-lock [in a submarine], into which the men enter to pass up to d a". Commented Feb 15, 2018 at 13:13
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    Yes, the aerospace term was inherited from the marine term, like aviation borrowed "fin". "Space" in the OED definition refers to (naval term) ship's spaces, not spaaaaaaaace like outer space. Commented Feb 15, 2018 at 23:43
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    If it was the space that made it be called an air lock then wouldn't it be called a space lock? Commented Feb 16, 2018 at 0:25
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    @immibis: "Space" in this answer refers to an enclosed place, not to outer space. In your hypothetical, we would call it a vacuum lock. Commented Feb 16, 2018 at 21:12
  • @Timbo Space in my comment refers to outer space, not to an enclosed place. Commented Feb 18, 2018 at 20:17

You could say 'watertight chamber'.

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    That customarily refers to separated segments below the waterline of a surface ship, meant to prevent a hull beach in one from flooding the entire ship and sinking it. For example, the Titanic was hyped as "unsinkable" because it had 16 watertight chambers – unfortunately, six of them flooded, which was more than the design limit for the ship. nationalgeographic.org/media/sinking-of-the-titanic
    – Steve
    Commented Feb 16, 2018 at 8:21

A related term is vestibule, which is a term for a specific place in Christian Church, but has become a general term for the space between the exterior door and an interior door. These areas are somewhat like an air lock, in that they transition between interior and exterior spaces. In this case, comfortable interior temperatures vs hot or cold outside temperatures. Most often seen in public and commercial spaces.

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    A "vestibule" is a related term, but it is wrong for an underwater airlock. Commented Feb 15, 2018 at 15:17
  • Vestibule doesn't necessarily refer to churches. many kinds of buildings have vestibules.
    – AJFaraday
    Commented Feb 16, 2018 at 11:50
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    @AJFaraday - Indeed. "I'm in an ATM vestibule with Jill Goodacre!" (Wondering if anyone will get that quote...)
    – AndyT
    Commented Feb 16, 2018 at 13:50
  • @MartinBonner, I suppose it's a Roman term I associate with the Catholic Church; being the place for vestments. Commented Feb 21, 2018 at 16:11
  • @JeffSacksteder : Yes, I can well believe vestments->vestibule and then generalized. The point is, this is not an answer to the question as asked. It's a perfectly sensible comment on the question though. Commented Feb 21, 2018 at 16:28

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