What was the most effective naval anti-aircraft gun of WW2?

[lwd]

I don't think your basic premise is well supported.

[dunmunro]

I don't think your basic premise is well supported.

I don't think anyone has ever attempted to quantify the differences between a pom-pom and a bofors before, so this premise has simply been ignored. The USN did compare the Bofors and pom-pom very carefully in a series of trials, yet did not note, in the BuOrd FC histories, any quantifiable performance differences, other than the Bofors' higher MV.

[delcyros]

One of the most important factors in light AAA fire- not the most decisive one but for sure important- is the ability to inflict very serious damage in an as short timeframe as possible.
While heavy AAA don´t require multiple, direct hits to destroy a soft target like an aeroplane, light AA typically requires a number of hits to bring down the enemy before it can reach attacking distance with either droppable ordenance or cannons.
This was established in firing trials against wrecked airplanes on both sides of the conflict but the approaches and conclusions drawn from these firing trials have been controversial.
It all boild down to three schools: Either increase the volume of fire, or increase the accuracy of fire or increase the damage per hit. In the real world, all three approaches were tried to a different degree by the fighting nations of ww2.

Thus volume of fire may is entirely justified to be important. By the end of ww2, KAMIKAZE airplanes posed a serious thread to US naval forces operating in the Pacific. The introduction of variable time fuses increased the likelyhood of heavy AAA to hit these targets while the additional mounts of fast firing twin and quadruple BOFORS 40mm mounts increased the volume of fire drastically in the same time.

Germany went with the 3rd approach. By 1940, they realised that heavy hitting power with low explosive effect on target isn´t really necessary to destroy a soft airplane, regardless of size but very powerful blasts have the best chances to cause a plane going down. Hence they introduced mine rounds to their Luftwaffe fighter forces, thin walled projectiles filled up with high explosive. By 1943/44 this type of ammunition played a major part in their attempts to stop the B17 raids over central europe.
The 37mm KM FLAK light AA is basically using mine rounds in AA role since 1941. If You look closer to the explosive content of the 37mm round You may recognize that there is much more high explosive (0.8lbs) in them than in other nations medium AAA and even more than in US late ww2 3"/50 RF heavy AAA (0.57 lbs with VT fuse and 0.77lbs with AAT).
Still, the KM didn´t extended it´s 37mm mounts later in the war in preference for extending 20mm quad and 40mm mounts, why?
Originally, the KM thought about it´s 37mm mounts to represent some kind of high velocity, medium firing, one hit-one kill "sniper" gun aboard. This phylosophy was found to be unsound in ww2, while true, you need to hit in the first place and volume of fire helps hitting.
The other guns mentioned were better. In the KM, they were provided for special mine rounds in the AA role in 20mm and 40mm guns, the larger burster effect now was augmented by the faster firing system over the previous 37mm mounts.

[dunmunro]

I just got confirmation that the error in the USN 40mm rangetables originates in the original document, and is not a transcription error.

[dunmunro]

A quote from the RP50 twin Bofors mount manual:

The Mark 5 mounting carries two 40 mm, Mk 11 water-cooled Bofors guns which fire H.E. shell with direct action fuzes at a rate of 120 RPM. per gun at 60 degrees elevation, and 140 RPM. per gun at 0 degrees elevation. These rates of fire should be maintained as near as possible on mountings in service. The shells are self destroying at approximately 3500 yards.

Capabilities and Tactical use of the mounting
The capabilities of the mounting vary, according to the type of director controlling it: either a CRBFD or a Simple Tachometric Director (STD) may be fitted. With the former, the mounting is auto-operated and can be used for both " blind " and ' visual " fire since the C.R.B.P.D. is fitted with radar Type 262. There is very little difference in accuracy between these two methods and both show a considerable improvement on previous equipments.

The maximum effective range of the mounting when controlled by the C.R.B.F.D, is 2,500 yards but fire against aircraft should be opened at 4,000 yards to allow for the rapid closing rate during the time of flight,

With the S.T.D., the mounting is again auto-operated but only visual fire is possible as radar is not fitted. Due To the limitations of the sight in the S.T.D. the maximum effective range is reduced to 1,200 yards and fire should be opened when the range is 3,000 yards.

Continuous fire is maintained, so long as the supply of ammunition to the loader is maintained

A present day aircraft will be destroyed by two direct hits and quite possibly one, although the neutralisation of a suicide bomber by disintegration before it can read own ship would certainly require more.
http://www.hnsa.org/doc/pdf/br1919.pdf

The pom-pom looks better and better and the differences between the Bofors and Pom-pom, in terms of effective range are really minimal, and maybe non-existent. The STD sight was equivalent to a USN MK51, and the very short effective range is quite interesting.

[Thorsten Wahl]

Some technical data from the 3.7 cm Flak M42 (technical state 1944) fully automatic quick charging gun

practical rate of fire 140 - 160 RPM

5 types of projectile Vo up to 925 m/s
weight of projectile 565-700 g

range for opening fire 4.0-4.5km
range of tracer depending on projectile up to 2.7 km
optimal firing distance 1.8 km

Burster device impact fuze with burster unit with 9-12 sec delay

[dunmunro]

The 37mm KM FLAK light AA is basically using mine rounds in AA role since 1941. If You look closer to the explosive content of the 37mm round You may recognize that there is much more high explosive (0.8lbs) in them than in other nations medium AAA and even more than in US late ww2 3"/50 RF heavy AAA (0.57 lbs with VT fuse and 0.77lbs with AAT).
Still, the KM didn´t extended it´s 37mm mounts later in the war in preference for extending 20mm quad and 40mm mounts, why?
Originally, the KM thought about it´s 37mm mounts to represent some kind of high velocity, medium firing, one hit-one kill "sniper" gun aboard. This phylosophy was found to be unsound in ww2, while true, you need to hit in the first place and volume of fire helps hitting.
The other guns mentioned were better. In the KM, they were provided for special mine rounds in the AA role in 20mm and 40mm guns, the larger burster effect now was augmented by the faster firing system over the previous 37mm mounts.

I wonder how these shells maintained structural integrity against the accelerations required for such high MVs?

[Bgile]

Why call them "special mine rounds"? Why not say that the standard explosive filler was greater than anyone else's similar weapon, such as the UK 14" shell?

I have to admit I don't quite understand why this could be done by the Germans and not anyone else, and why that filler wasn't typical in all HE type weapons on up through battleship guns. What were the tradeoffs and why just the Germans?

[dunmunro]

The USN 5"/38 AAC Mark 34 - weighed 55.18 lb and had an exceptionally large 7.25 lbs (3.3 kg) burster, or 13.1% of total weight. Typical burster weights were in the range of 6 to 10%, so a 1.64 lbs. (0.742 kg) shell with a 0.8 lbs. (0.365 kg) bursting charge is very exceptional.

[RobertsonN]

This question of the high bursters in some German shells has also puzzled me for a long time. For example, Whitley in his books on German battleships and cruisers, gives the burster of the 88 mm as 3.1 kg and that for the 105 mm as 5.2 kg. These amount to about one third of the shell weight. I've always assumed this was because these were pure AA rounds whereas the US 5 in was a DP weapon. The thin walled German AA shells would disintegrate on striking ships without exploding: 'berstfrei' as given in the results for some nose fused HE shells given by Whitley.

Can anyone confirm this rationale or know of a better one?

[tommy303]

I wonder how these shells maintained structural integrity against the accelerations required for such high MVs?

The German Minengeschoss were ultra high capacity HE rounds used primarily in anti-aircraft roles. The problem of structural integrity created by such relatively thin walled shells was overcome by using very high quality alloy steel formed by drawing and tempering rather than forging and machining for shells in the 2cm--5cm size range. In larger shells, such as the 8,8cm and 10,5cm, Flak M-Geschoss shells were machined but still made of very high quality steel alloys to maintain structural adequacy--they were thinner walled than the usual point detonating HE rounds used against surface targets, but not so radically thin walled as the smaller cannon rounds.

[RobertsonN]

Thanks for this very interesting information. I was beginning to doubt whether the figures were correct. In German sources, the Marine-Arsenal issue on Bismarck by Breyer gives the same burster values for 37 mm, 88 mm and 105 mm as Whitley. Paul Smalenbach in his history of German naval fire control says that the 105 mm could be used in the surface role against MTBs up to 10000 m but still using the AA fire control and time fuzed shells. This range appeared to be the limit for time fuzed shells. I did not follow what he said about the procedure for destroyers or greater distances. From Brennecke's book on the Bismarck, the recommended method for sinking merchant ships was for a skilled gunner at a range of 400 m to fire single 105 mm shots just under the waterline as the ship rolled and to move along the ship from compartment to compartment. At the same time a few 37 mm rounds were to be fired higher up, to let air out. Whether this was using standard AA rounds is not stated, and whether this procedure was ever actually applied in the course of the war is also not known to me (although it might have been a standard U boat method).

[RobertsonN]

The less powerful naval version of the 105 mm gun (with a limited AA capability) used on smaller warships fired a shell having the same weight (15.1 kg) but a smaller burster (3.8 kg as opposed to 5.2 kg in the AA round).

[tommy303]

Paul Smalenbach in his history of German naval fire control says that the 105 mm could be used in the surface role against MTBs up to 10000 m but still using the AA fire control and time fuzed shells. This range appeared to be the limit for time fuzed shells.

Yes that would be approximately correct for time fuzed shell. For larger ships or longer ranges, regular, non-M-Geschoss nose fuzed HE or base fuzed shells would have been used.

At the same time a few 37 mm rounds were to be fired higher up, to let air out. Whether this was using standard AA rounds is not stated, and whether this procedure was ever actually applied in the course of the war is also not known to me (although it might have been a standard U boat method).

Normally the M-Geschoss would have been ineffective against even a merchant ship's steel hull, so the rounds of choice would have been AP-tracer or APHE.

[RobertsonN]

A question that has sometimes puzzled me is why the KM30 37 mm were never replaced on the Scharnhorst and Gneisenau by the faster firing 42 or 43 models as in cruisers and destroyers.
Perhaps it was that they simply came too late to benefit the battleships. Alternatively, it may have been thought the older model was more suitable on the battleships: some of their disadvantages (insufficient stabilization in heavy seas and faulty electrics due to wetness) were less marked on very large ships and their advantages (significantly greater range and higher ceiling than the later 37 mm models) were more important on a battleship where aircraft usually stood off the target to give their bombs higher terminal velocity.
While I know this topic is about the best AA gun of the war, the poor AA defense of the Tirpitz when it was sunk stands out. In various raids in 1942, invariably between 2 and 5 heavy bombers (mostly Halifaxs) were lost per raid. Admittedly, in those cases, the Tirpitz was in the company of other ships. On the last raid, only one side of the Tirpitz was engaged (by the time the aircraft were on the other side the Tirpitz was badly damaged and capsizing) and that for about 7 minutes. The 15 in and 5.9 in barrage was probably only a distraction at best. Does anyone know of any confirmed cases of aircraft being shot down by guns of 5.9 in or larger during the war? During this time (7 minutes) the eight 4.1 in might have fired about 850 to 900 shells. At the usual kill rate of 2000 rounds per shot down aircraft this was simply not enough. The 37 mm would have also been in range for a short time, but a hit with one of these (0.8 lb explosive charge) while not insignificant was never going to down a Lancaster, which could absorb considerable damage and still make it home. The large battery of 20 mm, although of some value against Albacores, was useless against Lancasters at 12000 ft. Other factors may also have played a role: poor morale and perhaps transfer of more capable men to ships that were still active.
As a matter of interest, what chance do members think a contemporary US battleship (which had the best AA defence of all) would have had of surviving such an attack (by about 30 Lancasters with tallboys)?