20mm cannon as defensive armamment for American bombers

Discussion in 'Aviation' started by Jenisch, Jun 7, 2013.

  1. Jenisch

    Jenisch Active Member

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    #1 Jenisch, Jun 7, 2013
    Last edited: Jun 7, 2013
    It would be a good idea to substitute the .50s for 20mm cannons? It would definately affect the weight and bomb load, but I'm wondering how effective in self-defense the bombers would become.
     
  2. wuzak

    wuzak Well-Known Member

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    It would be a good substitution in turrets. No so good for flexible mounts.

    I think for a B-17, for example, if you were to use 20mm cannons in place of .50" mgs you would possibly lose the waist gunners instead of dropping the bomb load.

    Alternatively you would only replace the key guns - so the tail turret would be the first.
     
  3. riacrato

    riacrato Member

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    I think it was trialled with the B-17 in the position where you'd expect a 20mm to have the most effect: The rear gunner. But apparently wasn't considered worthwhile. One has to remember that a) usually a bomber's defensive gunner is already shooting at the most vulnerable part of a fighter: the front. The extra punch from a 20mm might not be worth it and instead more ammo to waste is more useful. And b) it seems to me that defensive armament for bombers is more about putting as much lead in the air as possible. To make life so miserable for any attacker that he will back off. Actual kills are rather rare.
     
  4. yulzari

    yulzari Active Member

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    #4 yulzari, Jun 7, 2013
    Last edited: Jun 7, 2013
    The thinking behind experimenting with a 40mm gun turret on the Wellington was to keep the day fighters out of range. Even with only 20mm cannon on the bombers the day fighters would have to stand further off until actually making an attack and could then be engaged over a longer period of time. Think of a 20 x 40mm A/A battery flying at 200 mph at low level. Ideally with other such batteries with overlapping fire.

    One purpose of a formation of bombers is not only to be able to bring more guns to bear onto a single attacker but also, while the aeroplane attacked has only a head on target to fire at, the others in the formation will have a variety of angles of attack. With cannon they can engage further out and thus get, not only a longer period firing at an attacking fighter, but also a greater variety of angles of view of the attacker.

    In a night bomber things could be different. On a typical NW European night gunners only normally saw a night fighter within range of a .303". Some rear gunners had a protocol not to fire but tell the pilot what maneuvre to take in the hope that they had not yet been spotted. Tracer fire would give away their position. Others preferred to use lots of tracer to scare the night fighter away. There were some who would only prefer the later twin 0.5" turrets if they had automatic gun laying 'Village Inn' radar as they could accurately engage further away ay night. Otherwise they preferred to frighten the night fighter with lashings of tracer from 4x.303" in the general direction of the night fighter even if they were unlikely to hit it.
     
  5. gjs238

    gjs238 Well-Known Member

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  6. drgondog

    drgondog Well-Known Member

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    20mm only suitable, with structural reinforcement, to nose and tail of US bombers. Too large for the turrets. Was effective in B-29 except for usual US jamming issues..
     
  7. vikingBerserker

    vikingBerserker Well-Known Member

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    The USAAF actually installed a 20mm in a B-10 in place of the dorsal gun. It was just too unwieldly to use.
     
  8. altsym

    altsym Member

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    I would imaging 'friendly fire' would come into play also. With all the confusion, perhaps other bombers in the formation would get hit.
    I'm theorizing that a few 50 cal hits into another B-17 generally no big deal, whereas a few 20mm HE hits could potentially be a huge deal.
     
  9. davebender

    davebender Well-Known Member

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    IMO that's not necessary. Even a single .50cal MG is a pretty good deterrent vs enemy fighter aircraft.
     
  10. Coyote

    Coyote Member

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    While the destructive power of the 20mm is nice, the higher rate of fire of the M2 is more desirable.
     
  11. Jenisch

    Jenisch Active Member

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    Well, the Japanese installed a 20mm in the Betty's tail. Kind of ironic, given that the other guns were usually 7.92 mgs. =P
     
  12. davebender

    davebender Well-Known Member

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    Tail is the most vulnerable spot. So if you're going to install a 20mm cannon that's where it belongs.
     
  13. Night Fighter Nut

    Night Fighter Nut Well-Known Member

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    I think it would be a bad idea. Limited on ammo and you would have to improve accuracy in order for it to be effective. The .50's could throw up a stream of lead for the other plane to fly through. Can't do that with a 20mm.
     
  14. evangilder

    evangilder "Shooter"
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    Well, you could, if you reduced the bomb load. It's all about trade-offs.
     
  15. wuzak

    wuzak Well-Known Member

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    Or reduced the number of guns - lose the hand controlled waist guns and the gunners, and you may get the rear turret's ammo back up to the same level.
     
  16. yulzari

    yulzari Active Member

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    I recall that was the argument used for the 12 x .303" Hurricane and the 4 x .303" turret over the 2 x .5" one. Taken to it's illogical conclusion it would be 36 x .22".

    The Bulgarians found the single 20mm cannon in the Dewoitine D520 to be so much better than any number of 7.92mm machine guns. Yes a 20mm cannon would have less rounds per kilo but equally would have a lower rate of fire so (number geeks can rerun innumerable 20mm v .5" threads) have at least the same weight of bullets per minute but less of this would be casing copper and more would be explosive and/or incendiary filling.

    The RAF went over to 20mm cannon turrets for the later Lincoln and Shackleton and the USA for the B36.
     
  17. altsym

    altsym Member

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    So whats the difference in # of rounds between a M2 50cal HS 20mm for one second burst? Something like 2 rounds I think.
    Typically, when B-17's were engaged by the enemy, how many total 50 cal rounds were fired on average from all guns?
     
  18. Balljoint

    Balljoint Member

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    20 mm might have been useful against the armored Sturmbock Fw-190.
     
  19. Glider

    Glider Well-Known Member

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    You would never get a 20mm in the back of a B17. It way too tight for space and if you did it could do little but fire straight back. A B24 has a lot more space in the rear and would probably fit but not a B17
     
  20. Jenisch

    Jenisch Active Member

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    If the B-29 operated in Europe, it seems that more 20mm cannons could be add without affecting the bomb load for targets in Germany. Add to the superior fire control system of the '29, it would be very good.
     
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