[Tessa]

Originally Posted by Silent Ace

have emerged because they had stopped a threat to them, but given the fact that the submarines are normally carried out during the war and an average of 20 hours when compared with other data presented here think that their maximum stay under water was 48 hours and the American and British submarines of similar displacement and number of crew members.

That is quite an impressive collection of reference and rare books there. I envy that you're able to read both of them in their native languages. Recently have noticed a large number of people selling rare or otherwise difficult to get u-boat books, sadly all but 1 that I've seen wasn't in German. Hard to justify paying $200-$400 for a book you can't read unless it's one that's mainly a photo collection.

I was lying in bed this morning and for some reason started thinking about the question of where/how they got 72 hours. Though there is no longer any question about the actual time, I was trying to figure out how they got the 72 hours in the first place. There are various fact intermingled to support my ideas, but this is purely my guess as to how they obtained such a large number based from certain facts we all know and hands on personal experiences with lab classes in high school/college and the basic scientific method:

1. These tests (likely) weren't performed under combat conditions, they would have been done somewhere safe to ensure that the test wasn't interrupted. Anyone that's had a chem lab or physics lab class can attest that when something is to be measured, any and all surrounding factors that could alter the outcome of the test are removed in order to get a clear result. Your results are based on the test being performed under ideal conditions, therefore they are correct but not practical. A MG42 was capable of firing 1,200 rounds per minute; but this never would have happened. With machine gun belts being on average 250 catridges the time taken to swap new ones in likely wasn't factored in the testing (probably made special belts of 2000 cartridges in order to ensure continous firing) and those barrels overheated frequently when fired for prolonged periods with pause or water.

2. Germany was very meticulous at keeping records of everything they did (which ultimately ruined them when the allies began liberating the concentration camps and from the documents were able to find out detailed everything that was done there) so once the number was found discovered it would have been well documented many times over.

3. Having a boatful of people sitting around reading or sleeping would not have produced CO2 very fast. It's like taking a direct flight from Berlin to Los Angeles, very long and boring so if you can sleep through most of it its not as bad. I imagine (pure conjecture) they had 1 or 2 subs full of people and had them submerge with someone on the boat and the surface keeping tract of time. Once people finally started to pass out, or a set # had passed out; or someone was actuall in imminent danger of dying they would surface and pop the hatch.

4. Math - if they didn't perform the real tests one could figure out with x number of people in y space, how long will it take for the CO2 to get to z level? While the resultant number would have been inflated compared to [3] it would have been mathematically verifiable, even though it would have been impossible to replicate those results on a real test, even under ideal [1] circumstances.

5. Since we can't speak to any u-boat engineers anymore, and unless you've got a book that details how they tested the u-boat (precisely what tests were done and how so that got the statistical numbers) I believe that the 72 hour vs 48 hours is theoretical vs realistic. U-278 could have stayed under water potentially a few hours more, but they have absolutely no reason to, given that the CO2 levels would have started to get very uncomfortable right then I doubt any captain would want to subject his crew to such an experiment in order to claim that his boat stayed submerged the longest. Something not practical at all during war time.

Using U-278 as the baseline, if we knew what CO2% they were at prior to them surfacing we could more correctly calculate a (realistic) maximum submersion time. By recording the CO2 measurements each hour one could easily enough exptropolate from a graph what the max would been given the slope of the line from the 40-48 marks. It would also be easy enough to find the amount of CO2 produced per hour and compute it against the amount of airspace in the sub, and come up (again a theoritcal, albeit much more realistic) with its maximum submersion time.

Just because no boat never dived for 72 hours doesn't mean that wasn't possible. Most cars are capable of hitting a max of 125-150 mph; but do we actually drive that fast?

While this is all my own theory drawn from certain facts and knowledge of methods used for testing to obtain a reference point; I believe that the real max dive time is somewhere between 50-60 hours in a real situation. Most crews didn't need to stay submerged more than 24 -30 hours, there would have been no reason for them to push the limits to find out what the boat was really capable of. Even if you had a boat that could dive safely to a depth beyond what dc's were capable of, having your crew sit there for 2 days hearing constant explosions (despite knowing that they were safe) would start to make people psychological ill. Every minute you're submerged the air quality gets worse, while a captain may lie at the bottom for another few hours in order to be completely sure they were safe to surface after 24 hours they were likely dead, or able to sneak away.