Effectiveness of Bomber Defensive Armament by Type and Location

[Darthtabby]

While reading up on the Tupolev Tu-2 I came across a post Shortround made in 2018 saying that the British estimated that a powered mount was three times more effective then an unpowered mount. This got me curious about the relative effectiveness of the various weapons mounts employed on WWII bombers. Not only the effectiveness of the different types of guns themselves, but also of the types of mountings used and the locations of those mountings (chin, tail, dorsal, ventral, waist, etc).

My interest in this subject is partly out of personal curiosity though one of the people working on a strategy game mod I am doing research for has expressed interest in studies on the topic if any are available. I also figured there might be other people on this board with an interest in the general topic.

 

[33k in the air]

Once it was demonstrated that head-on attacks were possible, nose armament became the most important, at least for daytime bombing.

For nighttime bombing, the tail gun position was usually the most important. Not so much for its ability to actively defend the aircraft, but as a look-out to warn of an approaching enemy night-fighter so that the pilot could take evasive action.

 

[pbehn]

People had huge hopes for defensive armament to allow a bomber to get through, just as they had huge hopes for their interceptors to stop all bombers getting through. It proved impossible to give a bomber, or a bomber formation enough defensive power to beat off attacks from defenders. Even with "fighter" versions of the B-17 carrying no bombs, they couldnt carry enough defensive power to survive enemy attacks. Even the ultra sophisticated defensive power of the B-29 was proved eventually to not be worth carrying apart from the tail guns.

 

[Thumpalumpacus]

Yeah, the idea of a bomber fighting its way into and out from the target was a nice theory.

Key word is "theory". Reality is a harsh mistress.

I'd imagine that the waist-guns on -17s, -24s, -25s, etc were probably the most useless. I get the idea, that filling the sky full of lead might deter enemy fighters, but let's face it ... fighter pilots earn their billets by being aggressive.

The American pullback from unescorted missions in late 1943 tells the real story: none of the bomber's guns were very useful against a determined foe equipped with modern fighters. The LW at that time had both: determined pilots and good a/c.

The bombers were difficult targets, but at the end of it all, without fighter escort, the bombers suffered, and hard.

 

[pbehn]

The few deep penetration raids that took place by the USAAF bomber forces in 1943 were prohibitively expensive for them, but they were also prohibitively expensive for the LW. The tactic of using single engined fighters in the main to protect the extremities and twin engined fighters to defend the interior didnt work. The losses inflicted on LW twin engine heavy fighters were too high for them to sustain, single engined fighters had to be used so they couldnt be sent to other areas.

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[Thumpalumpacus]

The few deep penetration raids that took place by the USAAF bomber forces in 1943 were prohibitively expensive for them, but they were also prohibitively expensive for the LW. The tactic of using single engined fighters in the main to protect the extremities and twin engined fighters to defend the interior didnt work. The losses inflicted on LW twin engine heavy fighters were too high for them to sustain, single engined fighters had to be used so they couldnt be sent to other areas.

I hadn't known the Germans had that defensive set-up. It makes sense, given the short range of Allied fighter-escorts of the day; it shields the -110s from dogfighting to launch werfers and cannon attacks.

If I'm reading you right, the bombers were able to somewhat defend themselves against twin-engines? I was under the impression that the 110s would stand off out of range of American .50s.

I'd always thought, from Jablonski et al, that 1- and 2- engine LW fighters operated more closely in concert, the former doing frontal attacks and the latter using rockets to break up the bomber formations. Perhaps I read wrong, or perhaps I read so long ago I'm misremembering.

 

[pbehn]

I hadn't known the Germans had that defensive set-up. It makes sense, given the short range of Allied fighter-escorts of the day; it shields the -110s from dogfighting to launch werfers and cannon attacks.

If I'm reading you right, the bombers were able to somewhat defend themselves against twin-engines? I was under the impression that the 110s would stand off out of range of American .50s.

I'd always thought, from Jablonski et al, that 1- and 2- engine LW fighters operated more closely in concert, the former doing frontal attacks and the latter using rockets to break up the bomber formations. Perhaps I read wrong, or perhaps I read so long ago I'm misremembering.

I was only posting about the start, in 1943. The twin engined fighters that opposed the first Schwinfurt-Regensburg raid came from all over north Germany, some as far as the border with Denmark, they had the range and the time to do it, some of them were nightfighters. It was the same strategy with the RAF using Blenheim "fighters" to guard the interior of the UK which also didnt work. It wasnt only allied fighters that had short range, the Bf 109 cant range over North Germany for long, you need a lot to form a "picket line" of defence.

The losses of US bombers at circa 30% shot down or damaged were completely unsustainable but the losses of twin engined LW interceptors were also unsustainable at about 10% shot down or damaged. If the USAAF had mounted a similar raid the next day the LW would have fewer interceptors facing the same fire, so losses would be the same or higher. Wiki isnt the best source but on the first Schweinfurt-Regensburg mission Fighter strength is quoted as Bf 109s. bf110, and Fw190, on the second Schweinfurt raid Bf110s are not mentioned, they were batted out of the game, but that means many more single engined fighters are needed stationed all over Germany, the LW had to withdraw them from somewhere else.

 

[Thumpalumpacus]

I was only posting about the start, in 1943. The twin engined fighters that opposed the first Schwinfurt-Regensburg raid came from all over north Germany, some as far as the border with Denmark, they had the range and the time to do it, some of them were nightfighters. It was the same strategy with the RAF using Blenheim "fighters" to guard the interior of the UK which also didnt work. It wasnt only allied fighters that had short range, the Bf 109 cant range over North Germany for long, you need a lot to form a "picket line" of defence.

The losses of US bombers at circa 30% shot down or damaged were completely unsustainable but the losses of twin engined LW interceptors were also unsustainable at about 10% shot down or damaged. If the USAAF had mounted a similar raid the next day the LW would have fewer interceptors facing the same fire, so losses would be the same or higher. Wiki isnt the best source but on the first Schweinfurt-Regensburg mission Fighter strength is quoted as Bf 109s. bf110, and Fw190, on the second Schweinfurt raid Bf110s are not mentioned, they were batted out of the game, but that means many more single engined fighters are needed stationed all over Germany, the LW had to withdraw them from somewhere else.

My understanding was that the Schweinfurt raid suffered losses to -109s/-190s both inbound and outbound, as the latter refueled/rearmed while the bombers were approaching or over the target.

I hadn't realized the -110s took such a drubbing. I've always thought they were used as stand-off fighters and kept out of range of the bombers' defensive armament. Something to chew on.

 

[pbehn]

My understanding was that the Schweinfurt raid suffered losses to -109s/-190s both inbound and outbound, as the latter refueled/rearmed while the bombers were approaching or over the target.

I hadn't realized the -110s took such a drubbing. I've always thought they were used as stand-off fighters and kept out of range of the bombers' defensive armament. Something to chew on.

Well it is a question of perception, they caused heavy losses but suffered losses too. 10% were not available for the next day or for any night time operations, I was discussing the first Schweinfurt Regensburg raid. The first wave encountered opposition on the way to the target then went to N Africa, they encountered very little opposition after bombing the target. It may have been a disaster to the USAAF, it wasnt much better on the German side.


In bomber loss rate terms 4% was considered the maximum that could be sustainned in long term operations, it isnt much different inn fighter operations. 100 twin engined fighters have a shoal protection by numbers, just as bombers have in high numbers against flack. If the interceptor numbers go down then losses go up, in the extreme case a single, twin engined fighter alone has little chance of doing anything except being shot down attacking a formationn of 300 bombers.

 

[Thumpalumpacus]

Well it is a question of perception, they caused heavy losses but suffered losses too. 10% were not available for the next day or for any night time operations, I was discussing the first Schweinfurt Regensburg raid. The first wave encountered opposition on the way to the target then went to N Africa, they encountered very little opposition after bombing the target. It may have been a disaster to the USAAF, it wasnt much better on the German side.

Checking my sources again, it was the disjunction between the Regensburg and Schweinfurt flight that gave the single-engine fighters time to land, rearm, and refuel.

In bomber loss rate terms 4% was considered the maximum that could be sustainned in long term operations, it isnt much different inn fighter operations. 100 twin engined fighters have a shoal protection by numbers, just as bombers have in high numbers against flack. If the interceptor numbers go down then losses go up, in the extreme case a single, twin engined fighter alone has little chance of doing anything except being shot down attacking a formationn of 300 bombers.

I get that. I just didn't realize the LW had lost 10% of deployed 2-E fighters. That too, aa you point out, is not sustainable.

 

[Darthtabby]

I am well aware of the importance of fighter escorts for daylight mass bombing raids. Nevertheless I am actually interested in the relative effectiveness and importance of the various weapons, mounts and mounting locations used on WWII bombers models. After all most of them did mount defensive armament of some sort.

 

[Greyman]

I don't think there's a comprehensive analysis out there. So many variables involved in the breadth of WWII aviation.

 

[Shortround6]

I was under the impression that the 110s would stand off out of range of American .50s.

This gets mentioned a lot but the truth is there were very few guns (ammunition) that would out range the US .50 to any extent.

The US .50 would actually out range just about all 20mm guns (the closest was the Hispano).

The German 30mm MK 103 would out range the .50 and a few of the really large guns (37mm and 50mm)

Again a nice theory, it just didn't work.

The problem was never the "range" it was the ability to aim ahead of the target so the bullets and the target meet at the same point in the sky at the same time.
The .50 had one of the best retained velocities and shortest times of flight to a given distance. Soviet 12.7mm was just about as good or maybe a bit better.

 

[ThomasP]

Somewhere on the internet . . . there is a US/UK government sponsored analysis that talks about the effectiveness of the defensive weapons, the different formations used, the different patterns of attack used, day vs night, etc. I do not know if I downloaded it, I will see if I did or if I can find it.

I do not remember all it talked about, but some of what I remember is:

Powered gun turrets were significantly more effective than free-swinging guns. The only location unpowered defensive weapons were effective was in the tail.

Prior to the introduction of the GGS: The .50 cal had a higher probability of shooting down or seriously damaging a Luftwaffe fighter attacking a bomber, if it scored a hit. However, the multiple gun .303 cal turrets, coupled with their higher rates of fire and increased ammunition loads, had a higher chance of scoring a hit. Exactly how effective the .50 cal was vs multiple .303 was difficult to determine as there was not enough specific information.

After the introduction of the GGS: It was clear that the .50 cal became the superior armament for the turrets, with the understanding that for future bombers the 20mm would be a significant improvement over the .50 cal.

In terms of the US vs the UK concepts as to the type of installation: It was found that the UK turrets, for the most part, were superior in terms of reliability to the US turrets. They talked about a number of items in the reliability, maintainability, service life, etc. The only 3 things I remember are:

1. US electric powered turret drives needed to be significantly improved. It was found on operations that a common complaint was the US electric turrets could become inoperative - often before reaching the target area - due to the weather conditions and overuse by the operator when scanning for bogies.

2. While the UK turrets (in particular the hydraulic drive types, whether in US or UK service) were significantly more reliable than the US turrets, the hydraulic type had the disadvantage of sometimes being the source of fires due to the hydraulic fluid being flammable.

3. The electric drive was preferred for future installation, because of weight and simplicity, if the reliability of the electric drive systems could be improved sufficiently.

Though it was clear that the larger caliber weapons were the best choice for future defensive systems, particular if GGS and radar aided FC systems were employed, the supply of sufficient ammunition was more problematic. A reference was made to US bomber crew complaints of running out of ammunition before the attacks were over, sometimes before reaching the target. Early-campaign, it was the tail gun position that usually ran into this situation, but the other turret positions also encountered this problem. Late-campaign - in the bombers that had increased ammunition supply for the tail positions - the situation of ammunition shortage was spread about evenly among the tail, top, and bottom positions. The nose turret was least likely to run out of ammunition.

The UK bombers, particularly the types with the feed track systems supplying ammunition to the tail from large bins in the center fuselage, seldom ran out of ammunition, and later in the campaign the tail turret ammunition was sometimes reduced or carried in a manner that would allow resupply of other turrets. (Note that the above applied to daytime UK operations. Night operations were different enough that they were included in a separate section comparing the day vs night operations.)

The introduction of the nose gun turret on the B-17 and B-24 had almost no effect on the attack methods used by the Luftwaffe, re the number of head-on attacks vs tail attacks only changed by ~2%, from ~43% head-on to about 41% (IIRC). Losses remained essentially the same for the Luftwaffe, as did the number of bombers shot down. This data was from Luftwaffe records and post-war debriefs of Luftwaffe personnel.

 

[33k in the air]

I am well aware of the importance of fighter escorts for daylight mass bombing raids. Nevertheless I am actually interested in the relative effectiveness and importance of the various weapons, mounts and mounting locations used on WWII bombers models. After all most of them did mount defensive armament of some sort.

There was an analysis in the 8th AF which showed the number of aircraft kill claims by gun position for B-24s. It showed the belly turret engaged enemy targets the least, which led to the recommendation of removing that turret (since that would also lighten the aircraft and improve its performance).

 

[A.G. Williams]

There is a book called Gunner: An Illustrated History of World War 2 Aircraft Turrets and Gun Positions, by Donald Nijboer, published by Airlife in 2001. This includes a diagram of the dispersion pattern of .50 cal bullets from the different gun positions of a B-24. The diameter of the bullet pattern at 600 yards varied from 15 feet (ball turret) to 63 feet (waist gun, firing through open window).

More generally, there is some comment on the effectiveness issue in Flying Guns World War II: Development of Aircraft Guns, Ammunition and Installations 1933-45, by Emmanuel Gustin and some other chap, also published by Airlife (which no longer exists) in 2003. This includes some comments on effective range of .50 cals, and the aircraft formations used. A couple of pieces of information from this: the USAAF bombers expended approx 40,000 rounds for every German fighter shot down (they claimed 12,000 rounds, but gross overclaiming was rife due to lots of gunners shooting at the same plane), while the US fighters used about one-tenth of the ammo for every German plane they shot down.

 

[Milosh]

This is from the book AG Williams mentioned.

Testing done by the USAAF found that the bullet pattern from a B-17 during ground testing had the following results for 12 rounds to 600yds:

ball turret > dia. 15' - 8.3mils
upper turret > dia. 21' - 11.7mils
chin turret > dia. 23' - 12.6 mils
waist(closed) dia. 26' - 14.3mils
side nose > dia. 34' - 18.7mils
tail turret > dia 45' - 25mils

For the B-24 it was:

ball turret > dia. 15' - 8.3mils
upper turret > dia. 20' - 11.2mils
nose turret > dia. 23' - 12.9mils (Emerson)
nose turret > dia. 35' - 19.3mils (Motor Prod.)
waist(closed) dia. 23' - 12.9mils
waist(open) dia. 63' - 35.6mils
tail turret > dia 35' - 19.3mils

taken from: "Gunner" ISBN 1-55046-332-2

**************************

Attacks and hits on B-17s and B-24s, Jan - May 1944

Distribution according to direction of origin in azimuth

B-17 % distribution of 3585 attacks and 441 hits whose direction could be determined

12 - 20.2/15.6
1 - 12.5/9.3
2 - 5.9/6.7
3 - 4.5/3.9
4 - 5.7/4.0
5 - 9.1-9.2
6 - 20.7/15.6
7 - 5.9/6.6
8 - 3.8/2.7
9 - 3.9/2.9
10 - 3.7/3.9
11 - 10.4/10.3

B-24 % distribution of 10425 attacks and 102 hits whose direction could be determined

12 - 21.6/17.6
1 - 12.7/8.4
2 - 3.9/5.2
3 - 2.9/5.4
4 - 3.0/3.6
5 - 7.7/7.8
6 - 20.7/15.6
7 - 19.6/20.6
8 - 11.0/6.9
9 - 3.1/2.0
10 - 6.9/3.4
11 - 11.9/7.8

Note: might not total 100% as the graphic was hard to read

 

[Darthtabby]

S Shortround6 Is there actually any noticeable difference between the .50 and the Hispano? IIRC most P-38s and some of the later Spitfire variants mounted both types of weapons, I'd have guessed they were very closely matched in terms of trajectories.

Also do you remember where you read about the Brits finding powered mounts three times more effective then unpowered ones? (I know you have mentioned that in this thread, but coming across a post you made about it a few years ago in another thread was part of what prompted me to make this one.)

T ThomasP Very interesting info. Do you remember anything about the title of that study?

33k in the air Interesting. I might have guessed it was the waist guns that engaged the least often, not the belly turret. My understanding was American heavy bombers in Europe tended to fly pretty high and the belly turret seems like it would have wide firing arcs. But I guess it makes some sense, after all you don't hear much about WWII fighters attacking while climbing at their target.

A A.G. Williams Fighter escorts requiring vastly less rounds to down an enemy plane isn't hugely surprising. I'd be a bit cautious about reading too much into that comparison though. I've heard that shipboard AA didn't down that many enemy aircraft but did help make their attacks less effective. I wonder if bomber defensive armament might have offered similar benefits by placing additional stress on attacking fighter pilots, thus reducing the opportunities for easy shots.

M Milosh Yeah, that B-24 distribution adds up to something like 125%. That being said if you takes those numbers at face value the percentages of attacks coming from 12 o'clock vs 6 o'clock are very similar. But if you make arcs out of 11/12/1 o'clock and 5/6/7 o'clock the ratio of front vs rear attacks remains quite similar for the B-24 but shows significantly more frontal attacks with the B-17 (~20% more).

 

[ThomasP]

Hey Darthtabby,

i do not remember at the moment, but I will keep looking for either a copy I may have downloaded or the original website and/or document. I have some info in my notes, but I will have to dig them out. (I have over 80 notebooks with info I collected in the years before the internet really got going, so it might take a while. )

 

[space dodo]

there are always blindspots that enemy pilots will figure out and take advantage of, no matter how many guns you put on an enemy like the luftwaffe will figure out how to adapt- just look at the schrage musik mounting. the best solutions are to go on night raids and have fighter escorts.