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U-flak

Discussion in 'Submarines and ASW Technology' started by Kai-Petri, Jul 20, 2003.

  1. Kai-Petri

    Kai-Petri Kenraali

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    [​IMG]

    On 31/08/42 U-256 (on her first cruise sailing from Kiel on 28/07/42 to proceed to Lorient via the North Atlantic) was seriously damaged by Whitley 'B' of Sq 502. The boat was nearly scrapped but it was decided to adapt her into a U-flak - a heavily AA armed boat intended to lure unsuspecting aircraft to a deadly trap. It was expected to stop heavy losses in the Bay of Biscay inflicted by Allied aircraft by deploying a number of U-flaks.

    Although U-256 was the first boat to be converted into a U-flak, the reconstruction was delayed. In the meantime, on 16/04/43, it was decided to convert U-441 in the same way. The third and fourth Flakvierling mounts available (20mm quadruple sets) and the first experimental 37mm automatic gun were installed on U-441. Also, a battery of 86mm line-carrying AA rockets was installed (but this idea proved unworkable). It is sometimes indicated that two additional single 20mm guns were also carried. The fuel capacity was limited to Bay of Biscay operations only. Only 5 torpedoes were carried - in the tubes - for self-defence (room was needed for additional gunners taken aboard).

    The U-flak boats were 4 VIIC boats (U-441, U-256, U-621 and U-953) that were modified to act as surface escorts for the incoming/outgoing attack u-boats operating from the French Atlantic bases. They had greatly increased anti-aircraft fire-power and were intended as aircraft traps.
    3 more U-boats were taken aside as additional U-flak boats (U-211, U-263 and U-271) but none of them was completed as Flak boats although conversion did certainly start on all of them. They were eventually returned to duty as traditional VIIC attack boats.

    First operations
    Flak-U1 or U-441 sailed on 22/05/43 from Brest on her 5th patrol commanded by KL Goetz von Hartman. On 24/05/43 U-441 was attacked by Sunderland 'L' of Sq 228, shot the aircraft down but got seriously damaged by aerial depth-charges and was forced to return arriving on 26/05/43. The effectiveness of improved AA weaponry was overestimated and resulted in ordering U-boats to pass the Bay of Biscay on the surface in groups. This in turn resulted in heavy losses due to the group tactics adopted by the Allied aircraft.

    Further actions
    U-441 as U-flak again sailed from Brest on 8/07/43. On 12/07/43 she was attacked by Beaufighters 'A', 'B' and 'V' of Sq 248 and ended up badly damaged with heavy casualties (10 men dead, 13 wounded) in spite of the initial heavy AA fire. U-441 returned on 13/07/43.

    U-621 was converted into U-flak in June 43, after being damaged on her 4th cruise, by Liberator 'Q' of Sq 224 on 31/05/43. U-621 as U-flak sailed on 29/08/43 and scored no success on her 5th one month patrol. After being reverted to a normal flak armament she was damaged by aircraft on 6th cruise, by Liberator 'A' of Sq 59 on 13/01/44.

    The number of U-flaks sometimes is given as greater than 7. The confusion may arise from the fact that many boats carried extended AA armament, including additional guns installed forward of the bridge (and therefore easily confused with U-flaks).

    In November 43 it was decided to convert all the seven U-flaks (not all completed) back to normal attack boats, fitted with Turm 4.

    U-flaks were not able to fulfill their assigned mission in the Bay of Biscay - mainly because of the group tactics adopted by Allied aircraft (one can see the irony in this). According to the German war sources only 2 aircraft were shot down by U-flaks (and some damage inflicted on others) in 6 U-flak missions (3 by U-441, 1 by U-621, U-953 and U-256).

    Because of the limited fuel capacity and torpedo load U-flaks were not suitable for normal operations. At the same time the standard AA armament for U-boats was no longer much inferior to U-flaks. This and lack of success made U-flaks somewhat redundant.

    http://uboat.net/types/u-flak.htm
     
    lwd likes this.
  2. TA152

    TA152 Ace

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    That was an interesting piece KP!! It kind of reminded me of the idea that the USAF had to convert a few B-17's and B-24's to carry extra guns and turrets to act as escorts for the regular bombers into Germany before the intoduction of the Mustang.

    That idea did'nt work either because after the regular bombers dropped their bombs the escort bombers still were loaded down with all their extra guns and ammo and could not keep up with the planes they were supposed to protect.

    I guess the submarine idea and bomber escort idea are more examples of stuff that looked good on paper but in practice were flops. :(
     
  3. Martin Bull

    Martin Bull Acting Wg. Cdr

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    The 'upgunned' B-17s were converted B-17Fs and were known as 'YB-40s' and I believe about 23 or 24 were built. As you rightly say, they were a failure due to the weight penalty.

    However, some useful features from this experiment were carried forward to the B-17G; namely the chin turret and staggered waist gun positions.
     
  4. wilconqr

    wilconqr Dishonorably Discharged

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    It is sometimes hard for me to imagine why Germany's U-Boot innovations took so long to develope. Why was the Swiss? Shnorkel thrown by the wayside and why was technology kept at such a standstill for so long as to not have had boats like the Type XXI much earlier. Notwithstanding all of the improvments made to "other" German weapons of the time, it seems (to me)that the
    U-Boot program suffered for a lack of interest (by powers outside the Kriegsmarine) for a dangerously long time. I think further work with the snorkel and longer lasting batteries would have been far more beneficial to the Boots than putting more external weapons on them (Flak). It is hard to imagine the Germans not seeing the innovations in radio (I.e. radar/sonar) as being on their heels to the point that surfaced boats would be at a much higher threat in the near future.
     
  5. C.Evans

    C.Evans Expert

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    Great information Kai--sorry I hadn't seen this thread earlier.
     
  6. Greg A

    Greg A Member

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    Very interesting Kai. U-Boats set up as an AA platform. Kind of like the Juneau that was an AA Light Cruiser the Sullivan brothers were on.

    I did also get recollections of the converted B-17s and B-24s being used as airborne battle cruisers.

    Greg
     
  7. Erich

    Erich Alte Hase

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    Greg, actually it was the B-17 only though the experiment was a failure as the units could not keep up with the rest of the B-17's in the bomber stream due to additional guns, ammo and men.

    During the retreat from the Baltic a special task force of U-boots under the direction of ? formed close knit units as they were traveling on the surface with a great amount of people. Their fla pieces came in handy as the Soviet l-2's and torpedo planes had to run the gauntlet of many 2cm and 3.7cm guns. I'll dig in my database and be more specific soon......

    from places unknown at the moment...

    [​IMG]
     
  8. T. A. Gardner

    T. A. Gardner Genuine Chief

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    The snorkel was a Dutch invention. The Germans didn't use it early in the war simply because it was deemed impossible to keep a submarine trimmed precisely enough to maintain a constant depth as was necessary to make the snorkel work. Two things changed this, one technical one tactical. The technical change was going from the snorkel providing intake air to the diesels directly to using the entire volume of the boat as an air source with the snorkel providing make up air. This allowed the breather head to go submerged momentarily without killing the engines. Better crew training allowed for maintenance of depth with sufficent accuracy to allow the snorkel to work.
    The other change was the need to avoid Allied air attack. So the snorkel became the method of choice in part because it was forced on the U-boat crews out of survival.
    The Walther boats using hydrogen peroxide (HTP) engines were treated by the Kriegsmarine as technical curiousities rather than serious projects until late in the war. The Type XXI suffered from a combination of disrupted war production slowing down deliveries due to shoddy workmanship, lack of parts and materials, bombing delays etc and from developmental problems with some of the systems intended for use on these boats.
    As for radar and radio usage, the Kriegsmarine on the whole saw these as potentially dangerous items that would reveal the location of their naval forces when at sea rather than as devices that allowed them to find the enemy and as warning devices. In radar the concentration was on fire control. Search sets all derived from Luftwaffe sets later in the war rather than from naval developments. Aside from this deeply ingrained doctrine on electronics within the KM, the Germans also suffered from a general lack of steady development in this field. The Allies got too far ahead and the Germans couldn't catch up.
    The odd thing is that the Japanese Navy did much better with radar and technology on their submarines than the Germans did. It was just a poor operational doctrine that crippled their effectiveness.
     
  9. wilconqr

    wilconqr Dishonorably Discharged

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    Reading yet another book about U-Boats four years later! Still, the Flak Boat strikes me as a Beavis and Butthead kind of idea. What were they thinking? That they'd send out less than a dozen of these things to taunt a handful of aircraft into fighting? Aircraft that, even with a thousand of these boats, could never be anything more than a scratch on the seemingly endless number of Allied planes. At least up-gunned B-17's and B-24's were there to protect other bombers during the attack. Was it that the Flak-Boat was intended to support other boats within an operational area or were they just haphazardly sent out in hopes of inflicting some damage on the Allied air forces?
     
  10. wilconqr

    wilconqr Dishonorably Discharged

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    Question.....How did self-compensating fuel tanks work on Type VII's? As fuel was pumped out of the tanks from the top, seawater entered from the bottom. Was there some sort of collapsible fuel bladder that kept the two seperate? How did this work?
     
  11. Liberator

    Liberator Ace

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    An interesting thread.

    U 256 was also attacked on Thursday 13 August 1942 by Liberator Z/120 (LV341) at 1125 hrs in position 5320N / 2242W. As the Liberator went into the attack it was sighted by the lookouts on the U-boat who mistook it for a Sunderland. U 256 crash dived to a depth of 110 metres, three depth charges were heard to explode, but the submarine suffered no damage.
     
  12. Richard

    Richard Expert

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    The U-Flak turm was a good idea but it was late in the the war they were had been better in 1942 as the deck gun was seeing little action as merchant ships were now equipped with 2cm guns mounted forward or aft section given them the power to hit back at a U-Boat on the surface.

    The snorkel was a looser at the time it came in to service as Allied radar detection would detect it. The XXI was indeed a new type of U-Boat but once again far to late in the day.

    The war had come six years to early for the U-Boats, how true that was and yet they fought like lions.


    I must drop in to this forum more often.
     
  13. Erich

    Erich Alte Hase

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    although not purely a Flak-U you can see that this rig was upgraded with the 3.7cm Zwilling and the shields for the upper deck 2cm have been removed

    [​IMG]

    U-889
     
  14. Richard

    Richard Expert

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    The 3.7cm gun only fired one shell at a time no wonder they were removed in favor of the quadruple 2cm 38/43 with shield, I think they fired 160 rounds.



    [​IMG]
     
  15. Erich

    Erich Alte Hase

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    but the hitting power was greater with fewer rounds. the Flakvierling you show was certainly first rate without a doubt.
     
  16. Richard

    Richard Expert

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    As I recall Allied planes would just be out of range and contacted the nearest Destroyer(s) interesting dilemma for the U-Boat hope the plane will come in to range to slug it out or dive for it and risk aerial bombardment
     
  17. Fred Wilson

    Fred Wilson "The" Rogue of Rogues

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  18. Erich

    Erich Alte Hase

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    just anoter some refits on U-Booten included a twin 3.7cm mount rearward and even some had a forward single 3.7cm mount, these were not actually U-Flaks though.
     
  19. Poppy

    Poppy grasshopper Patron  

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    Excellent pic there Erich...It looks like that mount would cause a lot of drag, was it still efficient- and what are those 2 tubes located under the Flak? Tres cool sub.
     
  20. Carronade

    Carronade Ace Patron  

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    Later in the war they came out with fully automatic 3.7cm guns, types M42 and M43, which probably denotes their year of introduction, and which were used on U-boats. They used 5- and 8-round clips, similar to a Bofors gun, with cyclic rates of 250rpm although the practical rate of fire was less.

    The tubes under the 3.7 held spare torpedos which could be struck below through the torpedo loading hatches after some of the 'eels' in the torpedo room had been fired. This assumed that the boat could loiter undisturbed on the surface for a time, which also became less feasible as the war went on.
     

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