Hi Richard,

There were a number of factors that determined the length of time a U-boat could operate including various consumables (fuel, lubricating oil, drinking / cooking water, water for the batteries, food and ammunition, especially torpedoes to name some of them), combat damage, equipment failure and medical problems etc. It depended on the type of the mission and there were a lot of exceptions but for a typical mission from one of the French ports to the Atlantic the mission was generally to proceed to your assigned area of operations, get there around a certain day and operate there as long as possible.

Generally fuel was the limiting factor but if the hunting was good you might well run out of torpedoes way before fuel became a factor.

They certainly knew a great deal about food consumption per man during a patrol. The boat would be stuffed with as much food as possible. Every nook & cranny was used for food storage including the only head on a Type VII and one of the heads on a Type IX. The food had to be placed in the boat in the reverse order it was going to be consumed with the fresh food last. Therefore you didn’t just put all of one type of food in one place etc., there had to be a mix of food such that whole meals could be prepared from it as the cook was able to get to it. Needless to say everyone wanted the food stored in the head consumed first so they wouldn’t have use the bucket in the engine room. Not only that but the Chief Engineer had a say about where the food was stored as when it was consumed he had to be able to balance the boat. It wouldn’t do to put it all in one place – it had to be spread out over the whole boat as best they could. At sea the smut (cook) had to provide the Chief Engineer with a daily log of how much was consumed as it affected his ability to keep the boat in trim. I am not certain what happened to these logs but it is a pretty good assumption that they were turned in at the end of the patrol so theoretically U-boat Command knew exactly how much food was consumed for every U-boat for every day it was at sea for the entire war – at least for those boats that returned to port.

The fresh food was generally gone in two weeks and some of it was spoiled before then. There were all kinds of food problems from time to time. When they got to the canned food sometimes some of it was already spoiled and I have read of several cases where the labels on the cans were swapped. Imagine the look on the cook’s face when he finds out that all of the canned fruit is really spinach etc. Sometimes the canned food actually burst due to pressure changes inside the boat. Peter Cremer described just such an event on a History Channel special I saw last night. There was another type of spoilage too. When the boat got back to port the crew was frequently allowed to take some of the choice items many of which were completely unavailable to civilians at the time on leave with them. This would be reported as spoilage but everybody knew it was going on. It was an unofficial perk and it varied from boat to boat though but it was a frequent event & points out that they rarely ran out of food on a normal patrol.

Fuel was the consumable most likely to be depleted during a patrol. It could last a long time on an uneventful patrol and it could be used up in a very short time on an eventful patrol. Once notified of the location of a convoy the U-boat might travel for a day or two at top speed just to try to catch it. Once it was found they might have to travel at top speed for a day just to get into position for an attack etc. The boats were frequently ordered to be at a specified place at a specified time and doing so might require traveling at high speed etc. Even the weather had an influence on fuel consumption. The U-boat Commander did what he thought best in order to comply with his orders.

Generally U-boats were required to send their position to U-boat Command daily and when they did they were also required to notify U-boat Command of the amount of fuel they had left and of anything else that would limit their endurance (equipment problems, low on torpedoes, fuel leaks etc.). When they got to the point where they only had about enough fuel to return home or they were out of torpedoes etc. they reported that and requested permission to return. If they could be resupplied at sea U-boat Command would tell them where to go, otherwise they would be given permission to return to base.

Frequently boats returning because of equipment failure or because they had run out of torpedoes etc. would be ordered to offload any excess fuel (and anything else needed by the other boats) to other boats in the area. For part of the war there were purpose built resupply U-boats referred to as “Milk Cows” whose job it was to resupply the fighting U-boats at sea. Other large boats were sometimes also used for this purpose. When looking at their reports fuel, lubricating oil and fresh water were the items most in demand. The Milk Cows had refrigeration (the fighting U-boats had very little refrigeration) and also had a small bakery aboard so they could provide some fresh food which was always welcome because theirs had run out but it wasn’t because they were short of food. There is an excellent book on this subject: White, John F. U-Boat Tankers 1941-45 Submarine Suppliers to Atlantic Wolf Packs. Annapolis, MD: Naval Institute Press, 1998. ISBN: 1-55750-861-5. Copyright: John F. White, 1998.

Additionally over the years I have seen some complete lists of food carried on a specific U-boat for a specific patrol that have been posted on one or more of the forums here. Try the search engine for this forum and the General Discussions forum & you should find at least one.

At any rate the calculations about consumables made while the U-boat was in port were frequently nothing like what actually happened on the patrol because of all of the variables with fuel being the most troublesome. Fuel leaks especially from combat damage were fairly common. Still from experience they knew about how long each item should last under a given set of circumstances and they did their best to deal with the exceptions. Fighting a war is after all about dealing with the exceptions as the plan is frequently the first casualty.

Regards,

Ken Dunn