AAA, from 45mm to 57mm: a missed opportunity or waste of resources?

[CharlesBronson]

I think for ww2 this range of calibers were too damn heavy for a dependable automatic weapon, in the 1950s the technology was advancing fast enough to obtain fully reliable automatic weapons in 57, 75 and 76mm. The pot war Soviet 57mm is particulary good example of a good design, cant tell if they were ever equipped with proxymity fuzes, probably not.

 

[Jabberwocky]

The Germans tried several 50 mm and 55 mm AAA designs, with a notable lack of success.

The nominal effective ceiling of 37 mm weapons was about 4-4500 m, but in reality it was closer to 2500 m with visual aiming. This created a AAA 'deadzone' - in reality, just a less than optimal zone for the light AA/heavy AA crossover, between 3000 and 4500 m where Allied medium bombers could operate.

Theoretically, a 50 mm class weapon was the solution to this, with a proper effective range of about 3500-4200 m, but the designs never quite worked right. The 5 cm Flak 41 was slow firing and heavy, and the ammunition was ill-suited to its requirements, with a smallish amount of HE filler and a tendency to tumble at high velocity.

The 55 mm Gerat 58 derivative was started with this in mind. They upped the M/V to 1050 m/sec and increased the HE capacity of the round by about 20%. The rate of fire suffered with the bigger weapon. With the five round clips used (which weighed over 30 kg each), the gun fired at about 60-70 rpm. This wasn't too bad though, as the single barrel 37 mm/40 mm class weapons really only had practical RoFs ranging from 60 to 120 rpm.

The Gerat 58 wasn't fully finished by the time the war ended. The actual design itself was reasonably solid though. It formed the basis for the post-war Soviet S-60 57 mm gun, which was a very successful design.

The 5.5 cm flak was reckoned to have an effective range of about 4000 m with visual aiming, about 5200 m when radar controlled. The weapon was very powerful, with a M/V of just over 1000 m/sec (compared to around 800 m/sec for the 37 mm flak and 880 m/sec for the Bofors).

 

[RCAFson]

The anti-aircraft artillery in calibers ranging from 45mm to 57mm was a rare thing during the ww2. Soviets were using the 45mm AAA in penny packets (mostly/exclusively on their ships), Germans have experimented with 5cm, British with 57mm.
MY questions being whether such weapons would've provided the combatants with better AA means, or those should be regarded as 'neither fish nor fowl', too heavy to replace the 37-40mm guns, and too weak to replace the heavier stuff?

WW2 AA can be divided into autocannon firing contact fuzed ammo and manually loaded cannon firing MT or VT ammo. ~75mm is the smallest shell size that can accomodate MT/VT fuzes. Below ~75mm shells typically used contact fuzes, and since these shells must strike the target, hit probability is low unless a very high volume of fire can be developed. Against a typical WW2 aircraft, a 40mm shell probably provided a high enough kill probability per hit that it would be more lethal than larger but slower firing autocannon.

 

[Shortround6]

That is pretty much the story. The 3in/75mm Proximity fuse becoming possible later in the war than the 4-5in/100-127mm proximity fuse. Now throw in that the 'rule of thumb' for gun size/weight was proportional to the cube of the caliber and a 50mm gun would be roughly twice the size/weight of a 40mm (and so would the ammo) and trying to make high cycle rate 50-60mm guns becomes rather difficult. They tend to get rather large and heavy pretty quick.

 

[cherry blossom]

Although all the discussion in this thread up to now has been on land based AA guns, there may have been a specific need during WW2 for a 45 mm to 57 mm automatic AA gun to protect battleships from torpedo bombers as I tried to mention in a previous thread http://www.ww2aircraft.net/forum/ww...40-mm-choose-36310-post994276.html#post994276. By 1944-5, torpedoes could be dropped from a fair height and at reasonable speed. 800 ft and 260 knots were recommended by the USN, causing the torpedo to fly about 1,000 yards after being released before entering the water. Thus the release point would be about 1,400 yards from the target ship. The torpedo bomber needed to fly for perhaps 20 seconds without banking to set the gyros. The bomber could evade by diving (I am not sure if the pilot could kick the rudder bar) but had to fly a fairly predictable path from about 3,500 yards out to the dropping point. Thus there was a need to get shells out to 3,500 yards quickly and Musashi in October 1944 could have benefited from replacing some of its 25 mm weapons with something like the German 55 mm Gërat 58.
I specified battleships because the constraint of space was more significant than weight for battleships. The Yamato Class had 40 triple 25 mm mounts with each weighing 1.8 tons (all weights from NavWeaps - Naval Weapons, Naval Technology and Naval Reunions - Navy Weapons) which could have been replaced by weapons with a much longer effective range. For example, the last battleship to be completed ( some time after the end of WW2) was Jean Bart, which was equipped with twin 57 mm Bofors in 16 ton turrets. Its near contemporary Vanguard had sextuple 40 mm Bofors in 21 ton mountings showing an alternative approach to the same problem.

 

[Shortround6]

The American Navy jumped the 50-57mm size and went for the 3in. However it took until several years post war for it to come into service.

The Japanese had a real problem because the 25mm was in no way, shape or form equal to 37-40mm guns and the Japanese fire control for even the triple mounts was rudimentary compared to later fire control for 40mm Bofors guns. Only a few triples had RPC. Please note that at the longer ranges good fire control is essential. American 40mm ammo took 8.5 seconds to reach 4200 yds. A 235mph airplane will cover about 1000yds in that amount of time. Time of flight for a 50-57mm round will be a bit shorter but the effective limit on range is more a function of fire control than Ballistics.

WHile much heavier than a Japanese 25mm the 40mm Bofors fired at about the same speed, used a shell about 3 1/2 times heavier and had a shorter time of flight to the "longer" ranges.

The German 55mm fired at about the same speed (most of the guns varied a bit and often fired at different rates of fire depending on elevation, I don't get too excited about the difference between 120rpm and 140rpm. It fired a much heavier projectile about 20% faster at the muzzle but this only cut the time of flight to 4370 yds ( a bit further) to 6.75 seconds. Our 235mph plane can cover about 775yds (about 59 plane lengths for a 39ft long plane) in that amount of time. So greater "effective range" without radar ranging and a good predictor/director is pretty much an illusion.