Type XXI U-boats in early 1943

Discussion in 'Alternate History Discussion: After 1900' started by M79, Sep 3, 2009.

  1. M79 Well-Known Member

    Jan 8, 2007
    What would be the consequences of Germany being able to field Type XXI U-boats starting in early 1943? Only a few appear at first and they do not compose more than a third of the U-boat fleet until at least early 1944. Longer range, much more quiet, and the basis for the first-generation attack subs after WWII.
  2. BlairWitch749 Banned

    Jan 17, 2009
    Long Island NY
    if they became extremely effective which is prolly asb the us would actually produce the spruce goose http://en.wikipedia.org/wiki/Spruce_goose

    but after dday the subs are doomed. they lose the french ports and thus safe acess to the atlantic. once returned to germany the british would create mass minefields in the channel and in the iceland gap and brutaly patrol them with destoryers.

    waste of resources they should build more tanks and fighters
  3. Bill Cameron Banned

    Oct 8, 2004
    The Allies aren't standing still either and Coastal Command sunk over thirty of them in the OTL anyway.

    On the Allied side you'd see more homing torpedoes produced, more use of MAD, escort levels kept up, and the like.

    The U-boats' main handicap, strategic/operational recon, still exists. You can't attack a convoy if you can't find it in the first place. The U-boats' main Achille's heel, communications, still exists too. The Allies still have Huff-Duff and are still reading Germany's mail.

  4. CalBear Your Ursus arctos californicus Moderator Moderator Donor

    Oct 4, 2005
    The allies win the war, probably sooner than IOTL

    Now, add in no Enigma breakthrough, just a bit less bad German luck at Stalingrad in September 1942, King getting more of his way in the War Planning department and...

    The allies win the war.

    Of course in this scenario we nuke Berlin, which would REALLY have pissed off Stalin, who wanted the place as a trophy, so it does have that going for it.:D

    In reality the Type XXI was a POS. Revolutionary design, great idea, lousy execution, more or less the entire German War Machine wrapped up in one leaking package. The Type XXI were so bad that only TWO boats out of 120 commissioned ever completed a combat patrol.


  5. Jukra Well-Known Member

    Nov 7, 2007
    Tuborg at Uborg
    True, mass introduction in 1944 is probably too late to have an influence. To have their submarines win the war after 1942 Dönitz should have been more forward looking. Tactical pre-war trials had exposed numerous problems with his concept of mass surface night attacks. Better weapons (acoustic torpedoes for self-defense) and better capability to underwater attacks did not require any drastic research breakththroughs but just more forward thinking. Additionally, it's curious that submarine mass production wasn't studied earlier although ship mass production was implemented already during the First World War.

    After 1942 I think only thing which could have made a real impact would have been earlier and better designed Type XXIII. Cheap, stealthy, deadly, suitable for anti-invasion defense. Of course delaying the Allied invasion brings it's own problems in atomic form.
  6. esl Member

    Dec 18, 2005
    Essentially correct. The problems associatied with the XXI were more to do with the 'emergency nature' of the programme at the end of the war. One could think of it as just one more attempt at another Vweapon. Without the allied bombing they would have been underway enmass by 1945 however differences in production tolerances meant that about 1/5 of the XXI had to be sent back to be rebuilt. In any other context more of a nusiance than anything else....so regarding them as POS is probably a mistake. They did become the pattern that all post war boats followed.
  7. Mote Well-Known Member

    Jan 22, 2008
    The biggest problem for the Type XXI is that the Allies were reading the German message traffic, so we knew when they were leaving port, where they were going, and often times where they were. This let us route convoys to avoid them and occasionally create fake convoys that were nothing more than hunter-killer group ambushes.
  8. esl Member

    Dec 18, 2005

    Type XXI was designed as a stand alone UBoat , which is one reason why the training took longer.

    It was equipped with the latest incarnation of the GHG passive sensor array with a steerable antenna that allowed baring accuracy down to 1/2°

    I was reported that during the war it was able to detect convoys at 100km +/- 50km and could place a wire guided torpedo with 20m of a aim point at 2km range. Thus it relied much less on communications than previous subs. It was also introducing a burst radio transmittion device to make radio intercepts much more difficult.
  9. Mote Well-Known Member

    Jan 22, 2008
    Which means that it won't be all that successful at intercepting convoys. Furthermore, still need to be telling your minesweepers to clear a path for the U-boat to leave port. One of our fun ways of finding and killing them.

    Radio intercepts were still being made even with the German burst transmissions and didn't we establish in the last thread that that convoy range detection was a load of BS? It's longer than post-war boats were getting against diesel snorklers a decade later, and snorkling puts a heck of a lot more noise into the water than any merchant ship's engines do.
  10. esl Member

    Dec 18, 2005
    The noise from a single ship or Sub doesn't compare at all to the noise generated by a convoy , its an order of magnitude higher and thus apples and oranges. Burst transmitions were not even ready before the end of the war so I doubt any one was interecting them either, especially since no XXI got into patrols before the war ended either :rolleyes: There are document cases of the Hipper detecting convoy 50km away and thats a surface ship which are much less effective using hydrophones.

    Radio Intercepts were of little tactical value in helping kill the sub.A type XXI was much faster underwater than the Type VII and much longer endurance. In tactical terms they were an order of magnitude harder to kill with ballistic ASW weaponary, which was every thing except the accoustic torpedos.

    HF/DF was of emence value in vectoring in enemy aircraft and Sub hunting patrols to attack them before they reached the Convoy. In effect it trippled or quadrulped the effective search sweep range against Uboats. Which on average was about 10 nm on the surface.

    In historical plane attacks , only 8% of the detected targets were attacked and sunk, the rest got away. If they were attacking type XX-I uboats, the figure would probably be more like 1-2% kills.

    Further more 3/4 of the Uboats sunk by aircraft alone, did so either on subs in port or in transit. Operational results indicate that only 1% of schnorkeling subs were detected intransit. In 1943 only 2 subs were sunk in port while 47 were sunk in port in 1944/45. To get that level of kill in 1943 , you have to have destroyed the LW by then. Meanwhile historically few of the Uboats had schnorkels in 1944 , infact only 1/4 of the operational boats had them by the end of 1944. The XX-I had scknorkel as did the XX-III , so most of these air kills & surface kills, would not have occured either.
    Last edited: Sep 4, 2009
  11. Just Leo Contrarian with a heart of gold

    Aug 19, 2009
    Per John Terraine, "The Right of the Line" "The fast schnorkel submarine had emerged from the Second World War technically, if not militarily, triumphant." One of 90 launched sortied and was about to fire at the surrender. Six Type XXIII boats sortied and sunk six ships. None were sunk or seen. Post-war trials determined only 6% were detectable on radar. Construction was scattered through Germany and sent to Hamburg by canal. The Dambusters destroyed the canals. The ferroconcrete Hamburg facility would have required a Grand Slam bomb or three. They were indeed pesky critters but out of time. Earlier delivery might have saved Hiroshima.
  12. CalBear Your Ursus arctos californicus Moderator Moderator Donor

    Oct 4, 2005
    And doomed Berlin, Frankfurt, Hamburg...
  13. esl Member

    Dec 18, 2005
    An alternative to the earlier Type XXI scenario.
    The keys to the Type XXI programme where greater submerged endurance through tripling the battery capacity and increased underwater speed through greatly increased electrical generator power allied to a more streamlined hull/turret plus a Schnorkel.

    The Type XXIII had an endurance of 175nm @ 4knots and top submerged speed of 12.5 knots. The Type XXI had submerged endurance of 285nm @ 6knots and top submerged speed of 17.2 knots. However the initial production model only reached 15.95 knots in initial test runs and the first models had to be cleaned up to reach ~17knots.

    All this was achievable through the existing Type VII Uboat as a retrofit package. In fact the original designs for the “Type I” Uboat in the early 1930s [pu111], was a Uboat with 8.5-9knots top submerged speed and submerged endurance of 160nm @ 4knots. While the Type VII prototype was design to get ~8.5 knots top speed submerged.

    By adding saddle tanks to increase surface endurance from 4800 –6000 nm, they sacrificed ½ knot off top speed. To reduce crash dive time from to 20 seconds, twice as much flooding slit area had to be adopted, resulting in another drop in the top speed of ½ knot. So the war production Type VIIC Uboats had top submerged speed of only 7.6 knots and an endurance of 80nm@ 4knots.

    Reversing both of these should raise the top submerged speed back to ~8.5 knots. Further removing the flak and deck guns along with all the railings should increase the top speed again by 7%, to 9.2 knots.

    [1] Finally a variable pitch propeller matched up to the existing generator should increase the top speed by 50% to 13.8 knots.

    [2] By 1943 all new Type VII could be produced with the upgraded generator putting out 580 hp instead of 375hp of the original generator. Combined this should further increase the top speed to 15.9 knots.

    [3] Replacing the existing ammo bunker and the bottom row of reserve torpedos with battery space would more than double the Uboat endurance.

    All the above comes from Rossler’s “The U-Boat” , considered by many to be ‘the bible’ on German Uboat development and technology. Its also where the 100km detection range for the GHG sonar comes from at the start of the war. In one case in 1940, passive sonar detection occurred at a range of 100 nm or 180 km.


    According to Rossler, Steps 1, 2 and 3 were proposed to increase the effectiveness of the existing Uboat fleet in 1944; however overhauling the entire Uboat fleet would cause a significant delay in the Type XXI production schedule, so it was cancelled.

    To change the history, all you have to do is have Walter working with Donitz in Uboat Development from the start of the war, as Donitz ideally wanted instead of being put in charge of Uboat ops. Walters emphasized that the key to Uboat success was high underwater speed and endurance from 1933 on. Given the mid war ASW crisis, Walter would then convince Donitz to push for earlier peroxide boat development, but in the meantime modify the Uboats as much as possible for higher underwater speed and endurance. So the initiative to beef up the Uboat flak through rebuilding the conning tower in 1942/43, would instead be replaced with an initiative to mount the Schnorkel Walter designed in 1933/34, inside a more streamlined tower with no armament. Along with welding over ½ of the flooding slit area, this should raise the top underwater speed to ~9 knots in 1942.

    Removing the bottom torpedo row and placing extra batteries in the vacated ammo bunker, should then double the submerged endurance to 180 nm @ 4 knots. These changes should leave the existing fleet of Uboats with 10 torpedos and a submerged Schnorkel endurance of ~ 6000nm @ 10-12knots and a dash submerged speed of 30nm @ 9 knots. Combined with deep diving, this should reduce allied ASW effectiveness to ½ of historical levels. Thus “Depth Charge” attacks should only be 2% effective while “Hedgehog” attacks would only be 4% effective.

    Read more on ASW effectiveness in the OG 51 reports…

    Instead of building the Type XXI Uboats in 1944, overhaul all the Uboats with the ‘variable pitch propeller’ mated to an ‘upgraded 580 hp generator’ to get to the >15 knot top submerged speed possible. Combined that should further drop allied ASW effectiveness to much less than ¼ of historical operational levels, so even the ‘Squid attacks’ late in the war would be only a few % operationally effective at sinking Uboats.

    BTW reportedly 4000 Mark 24 torpedos were built, but the order had been cut back from 10,000 , so that could certainly change in response to greatly enhanced Uboat fleet. However the Mark 24 ASW torpedo would have been no use against the Type XXI Uboat or such a notionally overhauled Type VII/IX Uboat fleet, because @ 12 knots it was far to slow.

    Mark 24 ASW torpedo.
    This site reports that the Mark 24 acoustic torpedo was introduced in 1943 and was too slow to catch the Type XXI Uboat .

    “Fido would have been too slow to attack the Type XXI U-boats and could be avoided by going very deep.”

    Top speed of 12knots @ 15minutes.
  14. Valdemar II Banned

    Jul 26, 2005
    Copenhagen; the Kalmar Union
    Interesting how would this effect Allied shipping and the war?
  15. Jukra Well-Known Member

    Nov 7, 2007
    Tuborg at Uborg
    I think the Donut was the problem instead of the solution. He was quite firmly fixed to the idea of 300 subs winning the tonnage war with massed surface night attacks. The requirement for high numbers led to adoption of Type VII as the main type of boat which had an impact upon flexibility of U-boat arm (in selection of operational areas).

    Perhaps this solution might be reached if the US was well prepared to face the assault on US coasts in 1942? Instead of success, operation Drumbeat meets abject failure. This might lead into earlier soul-searching within KM.
  16. Slowpoke Panned

    Mar 14, 2006
    Eastern 'Yurp
    That's because he (at least until 1941) tried to at least attempt to follow Art. 22 of the London Naval Treaty (which was a piece of fanciful nonsense, written by a bunch of big-gun fossils).