The US Balao-class and Gato-class submarines had enough provisions to stay on patrol for 75 days. Information on other long-range submarines has proved hard to find, although this site mentions British O, P and R class submarines had a range of 20,000 miles.

Were there any submarines of other navies (British, German, Japanese, Russian) which could stay at sea longer than this without being resupplied?

A few related questions:

  • Were submarines often resupplied at sea by supply ships so that they did not have to go to a port?

  • What is the most number of days that a submarine remained at sea during WWII without going to a port (i.e. were there cases where subs were resupplied by supply ships several times)?

  • Did navies during WW2 have regulations as to how many days a submarine could remain at sea without sailors getting shore leave?

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    I don't see how any human being could remain mentally sane after being confined in a submarine for 75 days or more. – Bregalad Nov 13 '17 at 14:25
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    Quick source concerning resupply without ports: Submarine Tender – justCal Nov 13 '17 at 14:27
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    @Bregalad Current-day US Sailors stay out on patrol for 3-6 months on some classes of submarines - submerged the entire time. No easy task, needless to say. – SnakeDoc Nov 13 '17 at 18:49
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    @Bregalad My understanding is the missile boats stay out for 3 months, and attack boats stay out for 6 (both stay submerged the entire time after leaving port) - Then the crew spends a few months back on shore once the patrol is over, doing training, etc. It's a rough life - submariners are considered some of the toughest sailors in the navy, and get some extras such as Hazard Duty Pay and better chow (food) for the conditions they're in. – SnakeDoc Nov 13 '17 at 18:58
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    @LarsBosteen - I'm saying the sub can stay out longer if you resort to cannibalism (extra food, and if you do it early, less mouths to feed). Also helps with oxygen and other essentials. Bad for morale though... – Scott Nov 14 '17 at 9:20

Not a "hard" answer, but more than a comment.

The German Type VIIC was the most common type of U-boat, but with limited range and endurance. Its fuel bunkers could keep the diesels going for 20-35 days non-stop at a speed of 10-12 knots (own calculation, using the various "range X at speed Y" data points given here and here).

The Type IXC/40 would, by the same token, have fuel for 57 days at 10 knots, non-stop.

We know from various sources (e.g. "Das Boot", Lothar-Günther Buchheim) that U-boats would "patrol" their designated areas at much slower speed, to conserve fuel. Stopping the boat for maintenance and repairs would further extend the solely fuel-based equation, while combat operations like closing in on a convoy (when a boat would run at high speed) would decrease range drastically.

Records for the longest war patrols were 97 days for a Type VIIC (U 552) and 225 days for a Type IXD2 (U 196). However it is difficult to ascertain whether a boat was resupplied at sea on any given patrol. (U 196 was part of a group of similar boats operating in the Indian Ocean, with a tender operating as supply ship and mobile base, so it's fairly safe to assume they were resupplied in one way or another.)

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    Good find on the 225 days. I wonder if the crew were still sane at the end of it... – Lars Bosteen Nov 14 '17 at 9:03
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    @LarsBosteen: After that 225 day patrol, U 552 returned to Bordeaux on October 23rd, 1943. Apparently the crew was sane, or at least fit to serve, enough to leave, after 143 days in harbor, for another war patrol that lasted 147 days. – DevSolar Nov 14 '17 at 9:14
  • @LarsBosteen WW2 submarines -- being diesel powered -- were "surface vessels that could occasionally dive". After all, the Type IX didn't carry a cannon mounted on deck for the jollies. en.wikipedia.org/wiki/10.5_cm_SK_C/32_naval_gun IOW, submariners would go out on deck, and could get fresh ait if the weather was good. – RonJohn Nov 14 '17 at 17:47
  • @RonJohn: Definitely not as in "lounging in the sun", as the boat would have to be ready to dive at all times. There is the watch on the tower, but there was preciously little time to be had on the deck itself, and I doubt that the mere sailors would get any. – DevSolar Nov 14 '17 at 17:58
  • @DevSolar I bet German sailors got to go out in shifts (mostly at night, but some during the day early in the war; not at all when the mid Atlantic "black hole" was finally filled) when the weather was good. Ditto Americans in the Pacific. – RonJohn Nov 14 '17 at 18:10

Japan built several of the I-400 class submarines, two of which, I-400 and I-401, were operational in early 1945. These enormous submarines had a 37,500 nautical mile range, over three times the range of a Gato submarine, so one can presume that crew stores would be present to keep the crew functional for a voyage of several months. There seems little point in building that sort of range into a submarine if the crew can't last as long as the fuel.

However, by the time the I-400's were operational, the war situation had changed to where the planned attacks on the Panama canal, Los Angeles, Washington DC and NYC were no longer considered to be practical.

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  • I just found out that the I-400 class you mention here could stay at sea for 120 days with a range of 1 to 1 1/2 times round the world (according to ww2pacific.com/i-400.html). – Lars Bosteen Nov 14 '17 at 12:56
  • Ah, thanks Lars - I kept looking for an endurance figure, just didn't look far enough. – tj1000 Nov 14 '17 at 14:56
  • You're welcome to edit your answer to include this info if you want. – Lars Bosteen Nov 14 '17 at 14:59

The Japanese built the largest submarines in World War II (52 out of the 56 submarines) of over 3000 tons). These were also able to stay underwater the longest, over 100 days, and carried the best torpedoes. Some 41 subs carried aircraft. The reason for these innovations was that the Japanese were operating in the Pacific, the largest ocean in the world.

Despite these advantages, the Japanese submarine fleet had two problems. The first was that the Japanese built onl 174 of them. The second, and more important reason was that they were used to fight warships, not merchant ships, and also to resupply isolated Japanese garrisons, so 128 of the 174 were lost in combat. The survivors were mostly new or training ships.

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