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According to this comment by Jon Copley a Marine Biologist as interviewed by Nexus for their show "He was right: Engineer who warned Stockton Rush about OceanGate talks to Nexus",

There has never before been a deep-diving submersible that has imploded during a dive. These vehicles are not new. The first vehicle to carry people into the deep ocean did so nearly a century ago in the 1930s. Over those many decades, these kinds of vehicles [deep-diving submersibles] have taken far more people into the depths of the ocean than the number of people who have been to space.

Since the video cited the 1930s, and showed a screen cap of The Bathysphere, which is a deep-sea submersible I would simplify the claim to "have more people used deep-sea submersibles to visit the deep sea, than used spacecraft to visit space"?

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    Do you know what definition of "deep sea" is being used? If hundreds of meters is the definition, that is self-evidently true. The number of naval submariners is much larger than the number of astronauts. If the definition requires going down more than 4,000 meters like OceanGate was doing, I doubt that's a true statement but would be interested in the accounting. Jul 11, 2023 at 5:24
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    Back in a prior millennium Atlantis Deep Explorer would take up to two passengers (w/crew of one) down 800 or 1000 feet just off Grand Cayman. The SWMBO and I did the 1000' trip. Comfortable and educational. Now scuba certified. 130' is enough without a submarine. (When the crew, singular, briefs you on emergency procedures you pay attention. No one is going to come get you and the depth off Grand Cayman far exceeds the crush depth of the vessel.)
    – HABO
    Jul 12, 2023 at 12:46

2 Answers 2

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From the question, I guess the deep sea is defined as 200 meters or deeper.

From Wikipedia, a definition:

The deep sea is broadly defined as the ocean depth where light begins to fade, at > an approximate depth of 200 metres (656 feet) or the point of transition from > continental shelves to continental slopes

and an historical fact:

1930: William Beebe and Otis Barton were the first humans to reach the deep sea when diving in the Bathysphere, a spherical steel pressure resistant chamber. They reached a depth of 435 m (1,427 ft), where they observed jellyfish and shrimp.

Simply seeing that there is (was) a huge market for oil&gas manned submersible, definitely yes, more people in submersible than in the space.

Space has been reached (today figure) by 628 people.

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There is little reason to doubt the claim.

There are several possible definitions of space travel. A relatively broad one considers any human who has reached Earth orbit. According to the list of space travellers on Wikipedia, 622 humans have done that as of May 2022.

The usual definitions of the deep sea is the body of water in an ocean in which the sunlight decreases notably in intensity. Of course the exact depth at which the deep sea begins depends on several factors, but 200 m is the generally accepted depth beyond which we talk about the deep sea.

The typical test depth of contemporary nuclear submarines, i.e. the maximum depth for a submarine during peace time, and the depth that submarines go to during sea trials, has been given as 300–450 m. For example, submarines of the Los Angeles-class have a test depth of 450 m, which is clearly already in the deep sea. With a typical crew of about 130 sailors, and with 64 ships that have been or still are in service, and assuming that each ship has reached test depth at least once during sea trials, this line of submarines alone has brought more than ten times as many humans to the deep sea than have been to Earth orbit.

But even if we restrict ourselves to the depths that can be reached only by submersibles and not by submarines (i.e. by vessels that need support of other surface vessels), there is strong reason to assume that the claim is true. There is a large number of different deep-submergence vessels that reach depths exceeding 1000 m. One notable example is the French DSV Nautile, which has a test depth of 6000 m. According to the website of the operator, the DSV has been deployed more than 2000 times under various circumstances. With a crew of three, this means that at least 6000 humans have dived on board of the DSV Nautile. While not every dive will reach the maximum depth, or even the test depth of the vessel, it's certainly not an infrequent thing to do for the Nautile. For illustration, this paper reports on eight dives between 3000 and 4200 m depth, executed in the time span of two weeks in 1985. This short observation time span alone would amount to 24 trips of humans to the deep sea.

To sum up: regardless of whether we use the conventional interpretation of deep sea as any depth beyond 200 m, or whether we extend this to an arbitrary depth of 1000 m or more, there are many, many different submarine and submersible vessels that have been deployed in hundreds or thousands of dives in the last 100 years or so. Hence, it's safe to assume that the number of trips to the deep sea made by humans exceeds the number of trips to Earth orbit by a significant factor.

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    The space statistics seem to count unique travellers, whereas for you deep sea data you seem to count number of person trips. This obviously, is not quite the same thing. I don't expect this would significantly change the answers, but it is worth pointing out.
    – TimRias
    Jul 11, 2023 at 12:12
  • I made the same error, counting the submarines, but the question is explicitly about submersibles... Additionally, each ship has reached test depth at least once during sea trials, true but it is unlikely to do the depth testing with full crew.
    – EarlGrey
    Jul 11, 2023 at 12:39
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    "the DSV has been deployed more than 2000 times under various circumstances. With a crew of three, this means that at least 6000 humans have dived on board of the DSV" - only if we assume no-one ever dived twice, so every dive was crewed entirely by first-timers. That seems very unlikely. Jul 11, 2023 at 16:29

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