British Anti-Aircraft weapons 1940

[DBS]

I know Otis has done a lot of good work on British AA locations in 1940, so not going to step on his shoes. I have agreed with him to start a little research on the performance of the weapons. The main sources used are a variety of books by Ian V Hogg. Normally I would be wary of using a single author (and still hopeful of tracking down some primary source material), but Hogg is probably unchallenged in his field, and a former Master Gunner of the Royal Artillery so probably as reliable as can be on British weapons in particular.

For BoB, we have the following weapons of primary interest (ignoring ship-board AA which would be a factor in harbours but is at present not modelled):

Lewis .303 or .30 (US surplus) AAMG - single mount
Hispano 20mm - not fully pinned down yet but seems to be improvised mounting of Hispano aircraft cannon
2pdr QF Mk 8 pompom on twin mounting
40mm Bofors
3" 20cwt
3.7"
4.5"

We will leave aside the Lewis and Hispano for the moment - and their performance will be the least controversial anyway.

The 1936 British Army definition of effective ceiling, at least for the 3" and larger weapons was the height at which an aircraft doing 250 mph could be engaged for twenty seconds of fire before the barrel elevation reached 70 degrees. The figures quoted below are, wherever possible, for 1940. There was a big difference between the effective ceiling achievable in 1940 with the predictors then available and No 199 time fuse, and later in the war with more advanced predictors and the No 208 fuse.

The 2pdr pompoms were a conversion of the Royal Navy weapon for use at static locations. Ordered in the late 30s, the order was greatly curtailed when the Bofors proved superior and the decision was taken to procure that instead. It would seem that all the AA Command weapons were supplied on a twin mount.

2pdr QF Mk8 twin mount
Rate of fire - 60 rpm per barrel (feed was from 14 round belts)
Maximum ceiling: 16,000 feet
Effective ceiling: 6,000 feet
Fired a 2lb HE tracer shell (Mk1T) - percussion fuse with tracer-ignited self destruct

40mm Bofors
Rate of fire - 120 rpm
Maximum ceiling: 16,500 feet
Effective ceiling: 5,000 feet
Fired a 2lb HE tracer shell (Mk4T) - percussion fuse with tracer-ignited self destruct

3" 20cwt
Rate of fire: 20 to 25 rpm
Maximum ceiling: 25,200 feet with 16.5 lb shell, 37,200 feet with 12.5 lb shell
Effective ceiling: 15,700 feet with 16.5 lb shell, 23,500 feet with 12.5 lb shell

Hogg notes that there were over 215 potential combinations of shell and charges for the 3"! (Legacy of being a WW1 vintage weapon). But the main AA natures in 1940 seem to have been the 16.5 lb HE and shrapnel shells (Mk2B and Mk2BT respectively), the shrapnel intended for low-level work. Some of the 3" weapons were optimised for low-level work, which seems to have involved mods to the mounting and sights.

3.7"
Rate of fire - 10 rpm (note this is the 1940 figure; later fuse setters and auto-loaders later raised the rate to 25 rpm, and indeed 32 rpm when proximity fuses came in and did not need fuse setting.)
Maximum ceiling: 41,000 feet
Effective ceiling: 23,000 feet (this was 1940 - later fuses/predictors allowed 32,000)
Fired 28lb HE (Mk1C) or shrapnel (Mk2C), the latter again for low-level targets.

4.5"
Rate of fire - 8 rpm
Maximum ceiling: 44,000 feet
Effective ceiling: 26,500 feet (again, 1940 figure; later capable up to 34,500)
Fired 54lb HE (Mk1C) or shrapnel (Mk2C)

Conscious have not yet tackled the PAC rocket/cable defences, which certainly contributed to the three kills against the nine Dorniers in the famous low-level raid on Kenley on 18 August.

Feel free to contest any of the above, but please note the key point about fusing and predictors which seriously affect performance in any given year, and improve steadily during the war. Even Hogg's data books tend to quote 1944 performance figures for weapons such as the 3.7" or 4.5", and you have to dig into the text of his more discursive works to get the 1940 figures.

[otisabuser2]

Cheers Dave,

funny how most books dismiss the PAC system as a novelty of little value.

It was used in anger once during BoB, to my knowledge, and as you say was credited with one kill to a low flying Dornier and damaged or nearly brought down some others.

As a result of the losses sustained on this raid, similar low level attacks were not tried again.

regards Otis

[Hard Sarge]

Intersting DBS

as you say, HARD to confirm, but I like those numbers

not sure we can talk the programmer into dropping the ranges by that much, but I am willing to give it ago

which some info on the GE weapons of later years would help (if I try to change the weapons in one, I want to change them in both)

but it makes sense, there had to be a reason why the B-25/B-26 could fly there missions at the alts that they did

keep it up

[HMSWarspite]

ORIGINAL: Hard Sarge

Intersting DBS

as you say, HARD to confirm, but I like those numbers

not sure we can talk the programmer into dropping the ranges by that much, but I am willing to give it ago

which some info on the GE weapons of later years would help (if I try to change the weapons in one, I want to change them in both)

but it makes sense, there had to be a reason why the B-25/B-26 could fly there missions at the alts that they did

keep it up

If the AA ranges are being looked at (and I agree they should be), bombing accuracy (with and without effective AA/Flak) also need to be looked in to. If we suddenly degrade AA without changing bombing, I suspect we will all cruise along at 25000 immune to all except bird flu!

[Nikademus]

Or worse.....at low altitude like in USAAF.

[Hard Sarge]

ORIGINAL: HMSWarspite

ORIGINAL: Hard Sarge

Intersting DBS

as you say, HARD to confirm, but I like those numbers

not sure we can talk the programmer into dropping the ranges by that much, but I am willing to give it ago

which some info on the GE weapons of later years would help (if I try to change the weapons in one, I want to change them in both)

but it makes sense, there had to be a reason why the B-25/B-26 could fly there missions at the alts that they did

keep it up

If the AA ranges are being looked at (and I agree they should be), bombing accuracy (with and without effective AA/Flak) also need to be looked in to. If we suddenly degrade AA without changing bombing, I suspect we will all cruise along at 25000 immune to all except bird flu!

And why would you think this ?

that is well with in range of the 88, the 105, the 88/41 and the 128

notice the 3.7 and 4.5 are both still able to reach 30 + later on in the war

it is still going to be Flak Bait City at most targets in BTR, and in BoB, go ahead and fly at 25 K if you want, you are not going to hit anything

the ranges in BoB are light 4000, med 10000 and heavy 30000, these changes would give us more leeway and also add in more gun types, then just light/med/heavy

[HMSWarspite]

ORIGINAL: Hard Sarge

ORIGINAL: HMSWarspite

ORIGINAL: Hard Sarge

Intersting DBS

as you say, HARD to confirm, but I like those numbers

not sure we can talk the programmer into dropping the ranges by that much, but I am willing to give it ago

which some info on the GE weapons of later years would help (if I try to change the weapons in one, I want to change them in both)

but it makes sense, there had to be a reason why the B-25/B-26 could fly there missions at the alts that they did

keep it up

If the AA ranges are being looked at (and I agree they should be), bombing accuracy (with and without effective AA/Flak) also need to be looked in to. If we suddenly degrade AA without changing bombing, I suspect we will all cruise along at 25000 immune to all except bird flu!

And why would you think this ?

that is well with in range of the 88, the 105, the 88/41 and the 128

notice the 3.7 and 4.5 are both still able to reach 30 + later on in the war

it is still going to be Flak Bait City at most targets in BTR, and in BoB, go ahead and fly at 25 K if you want, you are not going to hit anything

the ranges in BoB are light 4000, med 10000 and heavy 30000, these changes would give us more leeway and also add in more gun types, then just light/med/heavy

I meant for BoB rather than BTR. As long as we don't hit anything when at alt. I was just pointing out that the flak vs damage pairing is a game balence issue, and if changing one much you must look at the other!

I keep going on about this, but is the diminishing returns issue on ever increasing flak understood? I would love to know how the game rates the effectiveness of gun number 99 on a site vs gun number 9 (for example)

BTW does the >30000 bombing bug exist in BoB?

[Hard Sarge]

if, we made any changes to Flak, I am sure we would also look at how it may change the game

to be honest, I think the 30 K bombing bug is in the game, only you will not see it, since none of the GE bombers can reach that Alt

[otisabuser2]

Thanks DBS,

some nice info there.

Whether the guns in the BoB game go up or down in ceiling will depend on whether the programmers use max ceiling or effective ceiling. I suspect the ones in BTR use max ceiling for the 37mm.

I read from one source that the naval bofors shells were fused to explode at about 10,500 feet. This is well below their quoted max ceiling. I do not know whether this applies to the Army models too.

regards Otisabuser

[DBS]

Have now started looking at German figures. Interesting... definition of "effective ceiling" may be part of the problem. Westermann's "Flak" seems to suggest that the German definition was more along the lines of ballistically accurate fire - ie, when does loss of velocity, atmospherics, etc, start screwing up predictability of where the round will go, rather than meaningful engagement of target. Interestingly, the 88mm Flak 18 is normally quoted as having an effective ceiling of 26,000. Yet in Feb 1939, a German study of the Flak defences for the Reich, especially along the French frontier, assumed that an anti-aircraft belt based around the Flak 18 would force enemy aircraft to climb to between 19,500 and 26,000 feet. The inference would seem to be that they would only be truly safe at 26,000, but that they would be reasonably safe at 19,500 or more. This performance was nevertheless seen as well worth it, given that RAF pre-war doctrine assumed typical bombing heights of 10,000, and the Germans assumed that the increased altitude would degrade bombing accuracy and altitude stress the crews, even if they subsequently descended once clear of the belt.

The closest reference that I could find to the British 1936 definition was a German study of 1942, examining future performance requirements, that assessed the engagement window of existing heavy flak against a target at 29,500 feet; speed of target undefined, but presumably at heavy bomber speeds of say 200-250mph. The 88mm Flak 18 and 36 were judged to have a window of only 14 seconds, the 105mm to have 49 seconds, the 88mm Flak 41 and the 128mm to enjoy 68 seconds. At 36,000 feet (the Germans were worried about possible pressurised next generation aircraft), the 88/41 and 128 were judged to still have a window of 31 seconds.

The current 37mm height of 16,000 may not be too wild; in April 1941, Bomber Command judged a bombing height of 16,000 feet as desirable because of the threat of the 37mm, but it would seem fair to say that 12,000-16,000 was judged as the upper end of the 37mm threat window. The requirement for the 55mm flak was an effective ceiling of 15,000.

One real difficulty for BTR to model is the doctrinal limits often put on flak after the introduction of Herrmann's Wild Boars - eg in Jan 44 no flak engagement above 16,500 feet during night raids on Berlin, to allow the fighters free rein. Similar limits had previously been imposed over the Ruhr. This was linked with the discreditation of the flak as an effective defence; a bit unfair, but perhaps driven by German love of statistics. The fighters seemed to offer a better return, but of course it was easily forgotten that their effectiveness was linked to the AA searchlights. And by effectively banning flak engagement in such instances, the "poor" performance became a self-fulfilling prophecy.

Westermann makes the point that the 128mm batteries were regarded as elite and remained all-regular, unlike the other batteries diluted with volunteer and not-so-volunteer helpers.

Anyway, will post performance figures once I have done a little more digging, but from memory those in the game - at least post JCL mods - are pretty in accord with Ian Hogg's. As I said above, it may come down to different definitions of effective ceiling. In one book, Hogg points out that if one is being absolutely pedantic, there are three ceilings for any AA gun - maximum (absolute max to which the charge can throw the shell, without regard to any accuracy or fusing issues), effective (defined by accuracy and fuse time-out limits) and practical (the one at which one can actually engage a target for long enough to have a sensible chance of hitting); in more general usage he uses the term "effective" to mean "practical" at least for the British guns - thus the figures given at the start of this thread.

[DBS]

According to Westermann, the Luftwaffe had two types of barrage balloon - a 200 cubic metre version capable of flight to 6,000-8,000 feet, and a 77 cubic metre version used for barrages up to 3,000 feet.

Another interesting point from Westermann - the decline of the German balloon defences due to production shortfalls and perceived declining effectiveness. Production bottlenecks included the gas canisters and the winches, and consideration was given to using seized French and Italian balloons. In Jan 44, the Germans deployed 2,400 balloons, but by the end of the year had only half that number. Perhaps we should have limited balloon production during 1943, but then none from Jan 44, given that attrition of balloons in game is probably lower than in real life - no loss due to weather, accidents, etc. Will see if I can find any production figures.

As balloons fell out of favour and availability, apparently resort was made to permanent valley defences, stretching cables and nets (including fixed explosive charges) across valleys to deter low-level attack on key vulnerable targets. Obviously driven by having suitable topography near a factory or installation. Probably too difficult to model, but I suppose that if one had good evidence that site X enjoyed such defences one might consider a fixed "balloon barrage" only going up to 500 feet.

[Speedysteve]

Hi Dave,

Good info. Thanks.

'German Balloons' reminds me. Aren't the Heavy Barrage Balloons 'indestructable' as it stands in BTR?

Steven

[DBS]

Otis

I read from one source that the naval bofors shells were fused to explode at about 10,500 feet. This is well below their quoted max ceiling. I do not know whether this applies to the Army models too.

According to Hogg, the Bofors Mk4T shell could be fitted with one of two tracer elements - first self-destructed the round at 3,400 yards, the second at 5,500 yards. The latter of course equates exactly to the 16,500 maximum altitude he quotes for the Bofors, the former sounds very close (10,200 feet) to your source. Not clear on which was preferred, and whether Service differences in preference. Suspect static defences in particular might have preferred the shorter fuse if worried about spraying surrounding infrastructure with remnants of spent rounds. Certainly the RN in 1932 regarded the critical range for light AA as 2,500 yards, since that was seen as the optimum for starting to engage torpedo bombers to either induce them to drop early at 2,000 or greater, when reduced risk of hitting their target, or giving a good window of engagement( and thus probability of a kill) by the time they had closed to better torpedo range at about 1,200 yards.

Found a reference to a British Operational Research study of the performance of 20mm Oerlikons and 40mm Bofors against German low-level raiders attacking coastal targets; date not given but I believe must be mid or late war for a) the use of Oerlikons by the British Army, and b) the use of Operational Research, and c) use of Triple Gyro sight. Nor is the height or speed of the raiders given, but I assume very low-level. The target was a Ju88, so bigger and slower than a Jabo, but more robust. Anyway, first sighting of the target was assumed to be rarely at greater than 1,400 metres, and the whole engagement time assessed as thirteen seconds from sighting to last chance of a shot. The 20mm was assumed to get off fifty rounds at best, the Bofors seven or eight.

The percentages are for inducing at least an attack abort through damage (or kill obviously).

Basic sights 20mm vs crossing target - 3%
Basic sights 20mm vs headon target - 12%
Basic sights 40mm vs crossing target - 18%
Basic sights 40mm vs headon target - 20%
Triple Gyro sight 20mm vs crossing target - 17%
Triple Gyro sight 20mm vs headon target - 76%
Predictor sight 40mm vs crossing target - 35%
Predictor sight 40mm vs headon target - 39%

Although the short visibility window robbed the Bofors of its range advantage, it was still seen as the preferred weapon - I assume this is because the Triple Gyro may not have been widely available, and that notwithstanding its massive PK vs headon targets, such a scenario was seen as less probable than a crossing situation, where it was much less impressive. British Bofors had predictor compatibility from 1939 when the Kerrison No 3 predictor with power laying was introduced.

Also worth noting the aircooling problem - a sixty round Oerlikon drum might only last 7.5 seconds, but the barrel could not cope with much more anyway, save on naval mounts with water-cooling.

[otisabuser2]

Nice info DBS [:)]

According to Westermann, the Luftwaffe had two types of barrage balloon - a 200 cubic metre version capable of flight to 6,000-8,000 feet, and a 77 cubic metre version used for barrages up to 3,000 feet.

Just been looking for the alt for the Heavy Barrage Balloon in later BTR patch. Thought it went much higher than this. Anyone know.

Yes Speedy, it was also indestructable in the game.

I'm cool with the 16,500ft max alt for the Bofors in BoB, as this equates well with the 15,000 ft 37mm in BTR.

The manuals for both assure us that performance fo flak does degrade with alt.

Low balloons to represent hills/mountains. There's a thought !

regards Otisabuser

[Hard Sarge]

I'm cool with the 16,500ft max alt for the Bofors in BoB, as this equates well with the 15,000 ft 37mm in BTR.

I thought the range for the guns in BoB were
4000 Lt
10,000 med
30,000 Heavy

?

Ballons are 4000/8000

[von Shagmeister]

Hi Steve,

Aren't heavy balloons supposed to represent a barrage and therefore presumably all the ground crew necessary to maintain the barrage, ie hoist a new balloon if one is lost/destroyed.

von Shagmeister

[Speedysteve]

Hi VS,

Not as I knew it. If i'm mistaken then forget what i've said. I always thought that they were able to be put out of action?

Regards,

Steven

[Hard Sarge]

only hassle I got with that, is the "small" ballon is also a barrage, at least in it's title

so either both should be killable and needs to be replaced, or both should be non-killable

overall, I would say, kill them and make them be replaced ?

[Speedysteve]

Agreed.

Surely if a balloon is blown up then it needs to be replaced?

[otisabuser2]

Surely if a balloon is blown up then it needs to be replaced?

When we place a barrage balloon, we place the balloon, winch gear, inflation gear and the crew for this.
Most of the time the balloon is inflated, and kept up at low altitude, which prevents it getting blown away or about too much. When a raid is known to be coming, the height of the balloon is increased, hence the phrase "when the balloon goes up" for emergencies.

When the balloon is straffed by fighters, only the balloon itself is deflated/exploded. The winch, inflation gear and crew are still there on the ground 4000 feet below.

They generally have a stockpile of spare balloons and can float up another one in about an hour.

So a straffed balloon should not necessarily be a total destruction of the unit.

Even more contentious is when the balloon cable is struck by a plane. The cable pulls down the plane, by either the initial force on the wing or by the drag from the combined weight of the cable which now ingeniously has a parachute at either end.

The pulling of the cable, makes a small rip in the balloon, which releases it's gas and falls to earth to be recovered, repaired and used again. It's the cable which has gone in this case, not the balloon. [&:]

Ideally, the game should count each balloon destroyed when shot at or struck, but replace them at the end of the day. Gratis.

regards Otisabuser