In Mission Impossible - Dead Reckoning Part One (2023), Captain speaks to Officer in a submarine:

Captain: Officer of the Deck, ship status?

Officer: Ship's depth, 50 meters. Bottom, 72 meters. Clearance to the ice canopy, 21 meters.

Captain: Distance to deep water?

Officer: Two kilometers.

Why aren't "Bottom" and "Distance to deep water" the same in this context?

  • 15
    Ship's and sea-bottom depth, and clearance to the ice canopy, are vertical measures; distance to deep water is a horizontal measure. Commented Mar 17 at 14:08
  • 4
    "Distance (ahead) to water much deeper than (50 + 72) = 122 metres." Commented Mar 17 at 14:10
  • @MichaelHarvey wow we're deep. We must be at LEAST twenty thousand leagues under the sea!!! Commented Mar 19 at 15:45
  • @JohnFilleau: I wonder how many people recognize the title as a measure of distance traveled, rather than a depth?
    – supercat
    Commented Mar 19 at 17:41

4 Answers 4


72 meters is the vertical distance to the bottom.

2 km is the horizontal distance to a place where the water is deeper.

The two measurements are not related.

  • This doesn't add anything to James K's answer.
    – Stuart F
    Commented Mar 18 at 10:32
  • 4
    @stuartf Personally, I thought it was more concise and to the point, and thus more clear. If you don't agree, then don't upvote it.
    – Jay
    Commented Mar 18 at 12:21
  • 11
    @StuartF I disagree: I think JamesK’s answer is difficult to read and unclear. I knew the answer here and I struggle to find it in the middle of James’s explanations of various numbers that aren’t relevant to the question. I’m also a native English speaker. This answer is much more direct and relevant, and thus much clearer, than James’s. And on this site, it’s hard to imagine that anything could matter more.
    – KRyan
    Commented Mar 18 at 15:19
  • 1
    @StuartF Why waste time say lot word when few word do trick? (that's me agreeing, albeit tongue in cheek, that answers should not only be rated on content but also matter of factness). Thinking this answer is good does not equate to saying that James' answer is wrong; it's just not as good because it doesn't get to the point as clearly. And that's assuming you don't upvote both in the first place if you think they're both equally good.
    – Flater
    Commented Mar 19 at 5:47

This is technical language, but as it is movie technical language it may be wrong, or not how an actual naval officer would speak, but made up by the author of the screenplay.

The apparent meaning is that the submarine is moving underwater (and under a sheet of ice) at a depth of 50m. The sea bed is at 72m (22m below the sub) and the ice is 21m above the submarine (that suggests the thickness of the ice is 30m thick, which seems unrealistic, most arctic ice is a few meters thick at most). Perhaps it means that the bottom is at a depth of 50+72m. It probably doesn't matter much to the viewer.

The submarine would have to travel 2km horizontally to reach "deep water" (however this is defined, but 72m is not considered "deep")

A similar misunderstanding is common in the name of the novel 20000 Leagues Under the Sea. In that story the submarine travels 20000 leagues horizontally, not to a depth of 20000 leagues. (1 league is about 5km so 20000 leagues is much more than the radius of the Earth)

  • Do you know if the sea is 72, or 112 metres deep? I don't
    – James K
    Commented Mar 18 at 3:15
  • 4
    The ice may be a bit thinner. Depth is measured to the keel (bottom of the submarine), but clearance to the ice means distance from the submarine top. OTOH, ice floats, so not all of its thickness is underwater, only 87%. But you probably need to include a bit of safety margin to the clearance, to not scrape the ice by accident. All in all, could mean 10-15m of ice.
    – IMil
    Commented Mar 18 at 4:40
  • @IMil yes, and the underside of sea ice isn't particularly flat. A submarine might be concerned with the thickest bits (apparently called "keels", the underwater part of ridges) while a climate scientist might be concerned with the average thickness or something like that
    – Chris H
    Commented Mar 18 at 13:06
  • The sea bottom is 72 meters below where the sub is.
    – Lambie
    Commented Mar 18 at 16:39
  • But in your answer, you say the bottom of the sea is 72 metres under the ocean surface. Unless you happen to know the technical language (I don't) you can't be sure. But it doesn't really matter, it's just a movie
    – James K
    Commented Mar 18 at 18:13

Question re: Officer: Ship's depth, 50 meters. Bottom, 72 meters. Clearance to the ice canopy, 21 meters.

The ship is at a depth of 50 meters under the ocean surface.

The bottom of the sea is 72 from the ocean surface.

The ship would have to go down 22 meters more to reach the bottom.

The ship is 21 meters below the ice.

All these measures are vertical.

The bottom of the sea at 72 meters is not considered "deep" here.

The ship has to travel two more kilometers (horizontally) to reach a depth of the sea bottom greater than 72 meters. And we are not told how deep that would then be.


‘Bottom’ in this case indicates the vertical distance to the seafloor. It’s probably in reference to sea level in this situation, though the exact meaning is technically ambiguous as described, it could be in reference to the under side of the ice above the submarine, or even to the current depth of the submarine. Knowing the exact depth of the seafloor is important for ships in general, but it’s especially important for submersibles, because hitting the bottom is generally a very bad thing.

‘Deep water’, in contrast is water that is deep, usually as defined by some threshold. With no further context beyond the assumption that it’s in the ocean, the term usually refers to areas of the ocean that are not part of either a continental shelf or an oceanic plateau (which functionally means a depth of at least 200 meters in most cases). In this particular exchange, the question is asking how far until the submarine reaches such conditions. This is important in context because submarines are not particularly good for operating in shallow water, in the shallows they’re much easier to detect and they have much less ability to maneuver to avoid attacks.

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