Technology and Operations
This forum is for discussing technological & operational matters pertaining to U-boats.
Re: U480 A stealth Uboat
Posted by:
ThomasHorton
()
Date: October 03, 2009 05:33PM
From the Blair book
“In the classified report [the American evaluators] sent to the Chief of Naval Operations, dated July 1946, they wrote that while the Type XXI had many desirable features that should be exploited, it also had many grave design and manufacturing faults. The clear implication was that owning to these faults, the XXI could not have made a big difference in the Battle of the Atlantic. Among the major faults the Americans enumerated:
Poor Structural Integrity.
Hurriedly prefabricated in thirty-two different factories that had little or no experience in submarine building, the eight major hull sections of the type XXI were crudely made and did not fit together properly. Therefore the pressure hull was weak and not capable of withstanding sea pressure at great depths or the explosions of close depth charges. The Germans reported that in their structural tests, the hull failed at a simulated depth of 900 feet. The British reported failure at 800 feet, less than the failure depth of the conventional German U-Boats.
Underpowered Diesel Engines
The new model, six-cylinder diesels were fitted with superchargers to generate the required horsepower. The system was so poorly designed and manufactured that the superchargers could not be used. This failure reduced the generated horsepower by almost half: From 2,000 to 1,200, leaving the Type XII ruinously underpowered. Consequently, the maximum surface speed was only 15.6 knots, less than any ocean going U-boat built during the war and slightly slower than the corvette convoy-escort vessel. The reduction in horsepower also substantially increased the time required to carry out a full battery charge.
Impractical Hydraulic System
The main lines, accumulators, cylinders, and pistons of the hydraulic gear or operating the diving planes, rudders, torpedo tube outer doors, and antiaircraft gun turrets on the bridge were too complex and delicate and located outside the pressure hull. This gear was therefore subject to saltwater leakage, corrosion, and enemy weaponry. It could not be repaired from inside the pressure hull.
Imperfect and Hazardous Snorkel
Even in moderate seas, the mast dunked often, automatically closing the air intake and exhaust ports. Even so, salt water poured into the ship’s bilges and had to be discharged overboard continuously with noisy pumps. More over, during these shutdowns, the diesels dangerously sucked air from inside the boat and deadly exhaust gas backed up, causing not only headaches and eye discomfort, but also serious respiratory illnesses. Snorkeling in the Type XXI was therefore a nightmarish experience to be minimized to the greatest extent possible.†End of quote
So on paper the Type XXI should have been the best submarine of the time. If the Germans had the proper manufacturing capability the problems with the pressure hull and the diesel engines could have been fixed. The design of the hydraulic system being outside of the pressure hull is, in my opinion, a bad idea, just for the reasons listed in the Blair book.
Did the Type XXI have a reputation that was greater than the reality?
In the 1995 book “Count not the dead: The popular image of the German Submarine†Michael L. Hadley wrote “During both wars and during the inter-war years as well, the U-boat was mythologized more than any other weapon of war.â€
Perhaps the greatest capability of the Type XXI was the myth of the Type XXI.
Since only two of them were used in combat (if memory serves me correctly) we will never know how effective the Type XXI would have truly been.
“In the classified report [the American evaluators] sent to the Chief of Naval Operations, dated July 1946, they wrote that while the Type XXI had many desirable features that should be exploited, it also had many grave design and manufacturing faults. The clear implication was that owning to these faults, the XXI could not have made a big difference in the Battle of the Atlantic. Among the major faults the Americans enumerated:
Poor Structural Integrity.
Hurriedly prefabricated in thirty-two different factories that had little or no experience in submarine building, the eight major hull sections of the type XXI were crudely made and did not fit together properly. Therefore the pressure hull was weak and not capable of withstanding sea pressure at great depths or the explosions of close depth charges. The Germans reported that in their structural tests, the hull failed at a simulated depth of 900 feet. The British reported failure at 800 feet, less than the failure depth of the conventional German U-Boats.
Underpowered Diesel Engines
The new model, six-cylinder diesels were fitted with superchargers to generate the required horsepower. The system was so poorly designed and manufactured that the superchargers could not be used. This failure reduced the generated horsepower by almost half: From 2,000 to 1,200, leaving the Type XII ruinously underpowered. Consequently, the maximum surface speed was only 15.6 knots, less than any ocean going U-boat built during the war and slightly slower than the corvette convoy-escort vessel. The reduction in horsepower also substantially increased the time required to carry out a full battery charge.
Impractical Hydraulic System
The main lines, accumulators, cylinders, and pistons of the hydraulic gear or operating the diving planes, rudders, torpedo tube outer doors, and antiaircraft gun turrets on the bridge were too complex and delicate and located outside the pressure hull. This gear was therefore subject to saltwater leakage, corrosion, and enemy weaponry. It could not be repaired from inside the pressure hull.
Imperfect and Hazardous Snorkel
Even in moderate seas, the mast dunked often, automatically closing the air intake and exhaust ports. Even so, salt water poured into the ship’s bilges and had to be discharged overboard continuously with noisy pumps. More over, during these shutdowns, the diesels dangerously sucked air from inside the boat and deadly exhaust gas backed up, causing not only headaches and eye discomfort, but also serious respiratory illnesses. Snorkeling in the Type XXI was therefore a nightmarish experience to be minimized to the greatest extent possible.†End of quote
So on paper the Type XXI should have been the best submarine of the time. If the Germans had the proper manufacturing capability the problems with the pressure hull and the diesel engines could have been fixed. The design of the hydraulic system being outside of the pressure hull is, in my opinion, a bad idea, just for the reasons listed in the Blair book.
Did the Type XXI have a reputation that was greater than the reality?
In the 1995 book “Count not the dead: The popular image of the German Submarine†Michael L. Hadley wrote “During both wars and during the inter-war years as well, the U-boat was mythologized more than any other weapon of war.â€
Perhaps the greatest capability of the Type XXI was the myth of the Type XXI.
Since only two of them were used in combat (if memory serves me correctly) we will never know how effective the Type XXI would have truly been.
