Destroyers.....

[RCAFson]

Its not just webbs opinion. he is fleshing out and reaffirming those held by Rawlings and Fraser, and quote them to support his statements . And campbell does not say what you are claiming he does. In fact whilst Campbell does say alot about the technological operation of the weapon, he is pretty silent about its value (the 2pounder) . He does say, however that the type had serious problems with relatively low muzzle velocity, though some mountings and later gun types in the family did addresse this at least partially. As to common sense, well, thats a matter of opinion really, but a genuinely friendly piece of advice, I would not start running around spriuiking that this or that source lacks common sense. What do you think the other contributors would say if they were asked who was lacking common sense (and experience) in this debate....... for what it worth I think I am lacking in common sense and judgement for even getting mixed up in this debate..... .

Campbell, Naval Weapons of WW2, p. 67: "...if control and mountings were of equal efficiency, the Bofors was reckoned to be twice as effective as the pom-pom against torpedo planes but not much better against very close range targets such as Kamikazes."

The comparative service MVs of the Bofors/Pom-pom are 2720/2300fps - The Bofors will be more accurate and hit harder, but if a 40mm 2lb explosive shell can tear apart an airframe so can a 40mm 1.8lb explosive projectile as Campbell implies.

The Pom Pom could not operate as effectively as the bofors because of the limits of the gun. It was not a good area defence weapon at all really, which is why is was obsolete by wars end. It was shorter ranged and the loadout of the ammunition more restricted. It had some serious relaibility issues. Pom Poms, whilst better able to provide some cover fire over high value targets than a 0.5 or 20mm cannon, , were still too restricted in their effective range (at least in the DD fit outs) to do this job as effectively as the longer ranged and more lethal Bofors.

With self destructing ammo, the Bofors and pom-pom had roughly the same effective range. A well maintained quad pom-pom was also quite reliable and had the advantage of a large on-mount ammo supply, that could fire without reloading for over a minute. One could fit a quad pom-pom into the same weight of mounting, occupying the same deck area, as a twin Bofors.

no-one is saying that the 5/38-bofors combinination was completely effective. The USN thought it needed a heavier punch than either could deliver,m which is why they spent so much time and effort working on a 6" DP weapon. Determined Kamikazes could still penetrate the screens even with Bofors and 5/38 blazing away as hard as they could. But the british Admirals at the scene thought they had greater capability than their own equipment, which they saw as part of the problem, along with, as you say, the shortcomings in their DD radar fitouts.

Of course the larger and better armed late war USN destroyers had greater capability than existing BPF destroyers. The latest classes of RN destroyers were still working up in Europe as the war ended.

 

[RCAFson]

This commentary would suggest that by 1945, the USN and the theory of air defence had bypassed the RN and its oudated equipment.

I don't think that comparing 1945 designs with 1939 designs is very helpful. The last classes of wartime RN destroyers the C, Ch and Battle classes had improved FC with better radar, a modern CIWS outfit and RPC 4.5in guns - but they arrived just too late to make a useful contribution to the BPF.

 

[RCAFson]

There is some information on the philosophy of RN DD design with respect to anti-aircraft guns at http://www.royalnavalmuseum.org/documents/SB45_Autumn2012.pdf. It is too short but seems interesting.

Yes, an interesting and informative article by an RN officer:
Museum Model Series – Part 2: HMS Eskimo (Mark Brady) p.24

 

[parsifal]

Campbell, Naval Weapons of WW2, p. 67: "...if control and mountings were of equal efficiency, the Bofors was reckoned to be twice as effective as the pom-pom against torpedo planes but not much better against very close range targets such as Kamikazes."The comparative service MVs of the Bofors/Pom-pom are 2720/2300fps - The Bofors will be more accurate and hit harder, but if a 40mm 2lb explosive shell can tear apart an airframe so can a 40mm 1.8lb explosive projectile as Campbell implies.

I did see that quote, but only after Id made my original post. An omission on my part, but doesnt change much. Campbell is being very kind to the 2 pdr here. The problem is this. Kamikazes like all aircraft start out as long range targets. Unlike other forms of attack, they close at very high speed, and reduce the range to zero. They tend to attack so as to reduce the effects of centrally located weapon systems....for example, if the main defences are located aft, they will attack from ahead. This is probably why in those reports I posted earlier, the British ceased firing at critical moments. And unlike the Bofors, the 2 pounder mountings tended to be concentrated at one point on the ship. Kamikazes had an easier time blocking fire from 2 pounder mountings than they did against the Bofors mountings....poorrer fields of fire I guess.

However thats not the point. Whilst both the Bofors and the 2pounder had the same sized explosive shell, both had difficulty in destroying Kamikazes at close range. It usually took multiple hits to stop a kamikaze, and that required successful engagement from long range. Once a Kamikaze got to within several hundred metres of the target, unless it just missed, it was too late. For either of the 40mm mounts to actually stop a kamikaze, they really had to do it several thousand metres from the target. 2 pounder fire was much less effective at that, as Campbell points out. In other words, he was trying to be charitable to the 2 pounders. Again,i would point you in the direction of the commanders on the spot. they were clamouring for the Bofors to replace the 2 pounders for precisely this reason.

By way of comment, the USN even considered the 5/38 as lacking effective stopping power for a kamikaze, which is one reason they were working on a 6in DP weappon at the end of the war.

With self destructing ammo, the Bofors and pom-pom had roughly the same effective range. A well maintained quad pom-pom was also quite reliable and had the advantage of a large on-mount ammo supply, that could fire without reloading for over a minute. One could fit a quad pom-pom into the same weight of mounting, occupying the same deck area, as a twin Bofors.

I dont know about the self destruct ammo. but its just untrue that the Bofors and 2 pounders had the same range. again I refer you to the commanders on the spot. They simply dont back up the claims you make for the 2 pounder. And as you are so fond of quoting max ranges all the time, the max horizontal range of 10750m and a vertical range of 23000 ft, compared to the 2pounders maxs of 6800 and 13k vertical. They are not similar at all. If we want to be realistic and look at max effective range, the Bofors was about 4000 yards horizontal, and about 6000 vertical, the pom was about 2000 horizontal ( in the DD mounts that were deployed) and about 1800 vertiical. Again not comparable at all. Thats why the BPF wanted to ditch their 2 pounders and replace them with Bofors.

Of course the larger and better armed late war USN destroyers had greater capability than existing BPF destroyers. The latest classes of RN destroyers were still working up in Europe as the war ended.

In your following posts you mention Battle classes and various of the C classes. We have talked a lot about the Tribals and the JKN classes, and that I dont mind in the case of the tribals and the JKN, because these classes are within the spec of the original topic. Just to remind you, Luckys original list did not include any of the super exotic late war types, including the battle class or the Gearing classes for that matter. The best you could do would be to compare the Fletchers to the L M clases. Incidentally, all your rants about prewar US DDs are completely off topic because they too are not mentioned. Stay inside the specs of the original topic, or at least within the spirit of those specs.


This i would be happy to say. The USN, after developing truly war winning designs across the board in 1940-41 pretty much resisted further changes,, because at some point they rightly recognized the need for numbers. In the case of DDs the designs were so good, they really didnt go too wrong with that policy. With cruisers it was a different story. The Clevelands are the case in point. A workable design, but badly affected by topweight disease, in my opinion they should have brought forward the Worcesters and the DesMoines. These two designs give some indication of the vastly superior designs that could have eminated from the US if the need in the destroyer area had arisen. The British, with their Battles and C classes were simply playing catch up to the US DD designs. You have to go to the darings before you start to get a superior British design, and these really were true post war designs, and in any event were outdated before they were even commissioned.

 

[Shortround6]

The problem with shooting at a Kamikaze, as Parsifal says, is once it gets within several hundred yds it is too late, even with the pilot dead and large chunks of the plane missing it stands a good chance of hitting the ship someplace. It has gone "ballistic". This is why the 20mm, which was a fairly effective gun ( at least much better than .5in MG) in the beginning and middle of the war was considered almost useless against the Kamikaze. It could not inflict enough structural damage to the attackers to cause them to miss in the time/distance available. While the 2pdr shell may have been fairly effective once it hit the effective range was much shorter than the effective range of the Bofors, a combination of lower velocity and shell shape.

What would help is if any body has the time of flight to a given distance for both guns or the distance covered in, say 3 or 4 seconds of flight?

 

[parsifal]

I dont have that, but just to give some perspective to this, most common kamikaze was the A6M5. Kamikazes approached the tartget at the maximum possible speed in the final run.....for the A6M thats around 300-350 mph or about 12000 m per min. Thats 160m per sec.

The dedicated Japanese Kamikaze wasa the baka. This craft had a max level speed of 534 mph at sea level. Thats about 270 m/sec.


The known operational history of the Baka is intersting. The BPF fortunately never was targetted by this weppon. The US was hit , or targetted quite a number of times

"On 21 March 1945, 16 Ohka-carrying "Betty" bombers were to be escorted by 55 Zeros to attack Task Group 58.1 (Hornet, Bennington, Wasp, and Belleau Wood). Another two "Bettys" were to escort and provide navigation and observation. Due to technical problems, 25 Zeros had to turn back or could not take off. The Ohka attack force was intercepted by 16 US Navy Grumman F6F Hellcat fighters and the Ohkas were immediately jettisoned by the "Bettys," some 113 km (70 mi) from the target. None of the "Bettys" returned, no ships were attacked and 16 of the Jinrai Butai were killed, with only 15 damaged Zeros making it back to their base.

Attacks intensified in April 1945. On 1 April 1945, six "Bettys" attacked the U.S. Fleet off Okinawa. At least one made a successful attack, with its Ohka thought to hit one of the 406 mm (16 in) turrets on the battleship West Virginia, causing moderate damage. Postwar analysis indicated that no hits were recorded and that a near-miss took place. The transports Alpine, Achernar, and Tyrrell were also hit by kamikaze aircraft, but it is unclear whether any of these were Ohkas from the other "Bettys". None of the "Bettys" returned.

The American military quickly realized the danger and concentrated on extending their "defensive rings" outward to intercept the "Betty"/Ohka combination aircraft before the suicide mission could be launched. On 12 April 1945, nine "Bettys" attacked the U.S. Fleet off Okinawa. The destroyer Mannert L. Abele was hit, broke in two, and sank, witnessed by LSMR-189 CO James M. Stewart. Jeffers destroyed an Ohka with AA fire 45 m (50 yd) from the ship, but the resulting explosion was still powerful enough to cause extensive damage, forcing Jeffers to withdraw. The destroyer Stanly was attacked by two Ohkas. One struck just above the waterline just behind the ship's bow, with the charge punching completely through the other side of the hull before splashing into the sea and detonating like a depth charge, causing little damage to the ship, and the other Ohka narrowly missed (likely due to the pilot being killed by anti-aircraft fire) and crashed into the sea, knocking off the Stanly's ensign in the process. One Betty returned. On 14 April 1945, seven "Bettys" attacked the U.S. Fleet off Okinawa. None returned. None of the Ohkas appeared to have been launched. Two days later, six "Bettys" attacked the U.S. Fleet off Okinawa. Two returned, but no Ohkas hit their targets. Later, on 28 April 1945, four "Bettys" attacked the U.S. Fleet off Okinawa at night. One returned. No hits were recorded.

May 1945 saw another series of attacks. On 4 May 1945, seven "Bettys" attacked the U.S. Fleet off Okinawa. One Ohka hit the bridge of a minesweeper, Shea, causing extensive damage and casualties. Gayety was also damaged by a near-miss by an Ohka. One "Betty" returned. On 11 May 1945, four "Bettys" attacked the U.S. Fleet off Okinawa. The destroyer Hugh W. Hadley was hit and suffered extensive damage and flooding. The vessel was judged beyond repair. On 25 May 1945, 11 "Bettys" attacked the US Fleet off Okinawa. Bad weather forced most of the aircraft to turn back, and none of the others scored hits.

On 22 June 1945, six "Bettys" attacked the U.S. Fleet off Okinawa. Two returned, but no hits were scored. Postwar analysis concluded that the Ohka's impact was negligible with no US Navy capital ships actually hit during their attacks due to an extremely effective set of defensive tactics that were employed."

 

[RCAFson]

The range of a pom-pom at 2400fps = ? (~7200 yards?)
The range of a pom-pom at 2300fps = 6800 yds (Campbell)
The range of a Bofors at 2890fps = 11000 yds (USN range table)
The range of a Bofors at 2800fps =?

Bofors data: http://www.eugeneleeslover.com/USN-GUNS-AND-RANGE-TABLES/1956-4-1-0.jpg
Bofors range table: http://www.eugeneleeslover.com/ENGINEERING/OP1188/OP1188_Abridged_Range_Tables_1944.pdf (page 2)
Note that the above 40mm range table states that it is for 2800fps, but this is incorrect; it is actually computed for some other MV and this is easy to see since at 500 yards the SV = 2800fps, so the IV must be ~3200fps (V drop from 500 yds to 1000yds = 356fps). This is rather frustrating.
US Army data:

Ammunition: (for complete data, refer to TM 9-251 or TM 9-252)
Muzzle velocity:
AP-T shot and HE-T shell 2,870 fps.
Range (maximum):
AP-T shot, horizontal at 711.1 mils 9,475 yd.
http://www.hnsa.org/doc/boforstm/index.htm

This RN manual states that Bofors effective range = 2500 yds and 1200 yds depending on director type:
http://www.hnsa.org/doc/pdf/br1919.pdf (see introduction). Rounds SD at 3500 yds.

 

[RCAFson]

USN claimed kills in 1945: 40mm = 476.5.
5in = 380
20mm = 297.5

Credit for approximately 80 percent of all plane kills in suicide actions goes to the automatic weapons (50 percent to 40mm. and 27 percent to 20mm.), leaving 20 percent to 5-inch batteries, which fired disappointingly small quantities of ammunition at the many targets presented...

Although many ships have criticized the 20mm. as a defensive weapon against suicide planes, Tables V and VI indicate that it still is an effective AA. weapon both against suicide and non-suicide attacks. However, the 40mm. was by far the most effective weapon against suicide planes.
HyperWar: Antiaircraft Action Summary--Suicide Attacks [Chapter 2]

So if the 20mm was still effective, I guess the pom-pom was too.

 

[parsifal]

Not according to Webb, Rawlings , Fraser and a whole bunch of Allied Seaman that had to endure the japanese assault. But then, they havent written books that can be misused and misquoted 70 years later.

 

[Shortround6]

So if the 20mm was still effective, I guess the pom-pom was too.

Try reading the whole thing and look at the tables ( aside from a misprint or two, the table for 1.1 ammunition expenditures against non-suicide planes seems more than a little suspect).

"191 or 61 percent were shot down or deflected, but of these 53 or 17 percent, crashed close enough to ships to damage them"

That doesn't count ( and perhaps they didn't count) planes that were hit/damaged and actually hit the ships.

By the time a plane was close enough to "crash close enough to ships to damage them" the 5in was pretty much useless as was the 3in/50 so what was shooting down those 53 planes that crashed close enough to damage the ships?

40mm and under guns. While the 20mm can score a "Kill" for the chart if the ship is damaged by a near miss crash the 20mm has FAILED to protect the ship and so can be considered ineffective.

Having a 20mm battery that allows you to trade one destroyer out of commission for months for one or two attacking aircraft is hardly the way to win a war of attrition.

Maximum ranges mean very little because changes in projectile shape can have enormous differences in max range but a smaller difference in "practical" range.

Also please look at the materials you have presented. Some of the answers can be found there, it just takes a bit of digging and interpretation. Army and Navy 40mm shells were the same. Self destruct on those shells with it was about 5000yds which rather limits the "practical" AA range to that as a MAXIMUM.
However look at the navy range tables. Time of flight to 5000yds is 11.27 seconds and speed is down to 915fps. a 300mph airplane is doing 440fps so for the 40mm to "HIT" at that range the gun had to aimed and fired at point in space 4958ft ahead of where the plane was when the gun went off. When our valiant gunners see the puff of smoke from the self destruct burst it tells them where they should have been aiming 11.27 seconds ago. 5000yds is hardy a "practical" range for the 40mm gun.Also please note that 1/2 that distance (2500yds) the time of flight is 3.92 sec 35% of the time of flight to 5000yds. This is a much more "effective" range for the 40mm.
Please note that the 20mm has a time of flight of 7.27 seconds to 2500yds or about 85% longer.

The extra 500fps or so of the 40mm Bofors may be good for an extra 500yds practical range while a difference in the projectile shape may be good for another 500yds or so. You can change the "Max range" of a WW I/II military rifle by close to 2000 yds just by changing the shape of the bullet. The change in "practiacl" or "effective" range is much less but you cannot assume all projectiles are created equal.

 

[tomo pauk]

The maximum slant range really tells nothing about the effective range. The 30 mm AAA I've served on were to have some 9600m max range, but the self-destruct mechanism was igniting the shell after some 4,5 sec (ie. the max range was only applicable for the AP round). The effective slant range was 4000 m, effective altitude was 3000 m. That's a projectile of 430g fired at 1000 m/s (3280 ft). We were told by instructors that 3 shells are sufficient to kill a mid-sized jet, like MiG-21 or F-16.

The 20mm in the JNA was far less powerful, the practical range of only 1500m, for shell of 130-140 g fired at 830-850 m/s. (here, the 20mm).

 

[stug3]

HMS Encounter sunk along with HMS Exeter and USS Pope on 1st March 1942, her crew were stranded in the waters of the Java Sea for almost 24 hours until rescued by the Japanese Navy.

U.S. Navy Clemson-class destroyer USS Pope (DD-225) in January 1924, sunk by Japanese dive bombers on the 1st March 1942.

 

[RCAFson]

Try reading the whole thing and look at the tables ( aside from a misprint or two, the table for 1.1 ammunition expenditures against non-suicide planes seems
Also please look at the materials you have presented. Some of the answers can be found there, it just takes a bit of digging and interpretation. Army and Navy 40mm shells were the same. Self destruct on those shells with it was about 5000yds which rather limits the "practical" AA range to that as a MAXIMUM.
However look at the navy range tables. Time of flight to 5000yds is 11.27 seconds and speed is down to 915fps. a 300mph airplane is doing 440fps so for the 40mm to "HIT" at that range the gun had to aimed and fired at point in space 4958ft ahead of where the plane was when the gun went off. When our valiant gunners see the puff of smoke from the self destruct burst it tells them where they should have been aiming 11.27 seconds ago. 5000yds is hardy a "practical" range for the 40mm gun.Also please note that 1/2 that distance (2500yds) the time of flight is 3.92 sec 35% of the time of flight to 5000yds. This is a much more "effective" range for the 40mm.
Please note that the 20mm has a time of flight of 7.27 seconds to 2500yds or about 85% longer.

I explained, in my post above, how the USN 40mm range table was incorrect, so the data in it is useless. I presented a Royal Navy manual showing that 40mm SD range = 3500 yds and Campbell states the same.

The point is that the effective ranges of a Bofors and Pom-pom are identical, and the pom-pom has a longer effective range than the 20mm.

 

[Shortround6]

I explained, in my post above, how the USN 40mm range table was incorrect, so the data in it is useless. I presented a Royal Navy manual showing that 40mm SD range = 3500 yds and Campbell states the same.

No, what you showed was that initial entry in the striking velocity column was wrong. This may mean that some or all of the entries in the rest of the column is wrong or displaced by one line. Could be a simple typo. It does not follow that all of the rest of the data is wrong.

Time of flight to 500yds for the 20mm in the same publication. 0.66 seconds. Times of flight to 600yds for .30-06 M2 ball = 0.88 seconds, for .30-06 M1 BT =0.86 seconds, for .50 ball 0.72 seconds and for 20mm ammo 0.84 seconds. This last is a little off from the range tables shown but fairly close.
Time of flight to 500yds for the 40mm Bofors. 0.57 seconds.
Time of flight to 500yds for the 1.1in AA gun = 0.61 seconds.
Time of flight to 1000yds for the 40mm Bofors is 1.23 seconds
Time of flight to 1000yds for the 3in/50 mv 2700fps is is 1.18 seconds

Times of flight given for the 40mm Bofors are quite consistent with other rounds.

Going back to the British manual for the 40mm there is a dramatic difference in effective range depending on the type of fire control provided. This relates to the time of flight and difficulty in aiming (predicting) were the target aircraft will be several seconds after the gun is fired. The better your fire control the longer into the future you can predict the targets path (mainly because you have been tracking it's previous path more accurately).

Picture from Anthony Williams excellent website.

and

and

The point is that the effective ranges of a Bofors and Pom-pom are identical, and the pom-pom has a longer effective range than the 20mm.

Unless you repeal the laws of physics there is no way a slower, blunter shell has the same time of flight to a given distance or the same effective range as the faster, more streamline shell given the same level of fire control.

 

[RCAFson]

No, what you showed was that initial entry in the striking velocity column was wrong. This may mean that some or all of the entries in the rest of the column is wrong or displaced by one line. Could be a simple typo. It does not follow that all of the rest of the data is wrong.

Time of flight to 500yds for the 20mm in the same publication. 0.66 seconds. Times of flight to 600yds for .30-06 M2 ball = 0.88 seconds, for .30-06 M1 BT =0.86 seconds, for .50 ball 0.72 seconds and for 20mm ammo 0.84 seconds. This last is a little off from the range tables shown but fairly close.
Time of flight to 500yds for the 40mm Bofors. 0.57 seconds.
Time of flight to 500yds for the 1.1in AA gun = 0.61 seconds.
Time of flight to 1000yds for the 40mm Bofors is 1.23 seconds
Time of flight to 1000yds for the 3in/50 mv 2700fps is is 1.18 seconds

Times of flight given for the 40mm Bofors are quite consistent with other rounds.

Going back to the British manual for the 40mm there is a dramatic difference in effective range depending on the type of fire control provided. This relates to the time of flight and difficulty in aiming (predicting) were the target aircraft will be several seconds after the gun is fired. The better your fire control the longer into the future you can predict the targets path (mainly because you have been tracking it's previous path more accurately).

Unless you repeal the laws of physics there is no way a slower, blunter shell has the same time of flight to a given distance or the same effective range as the faster, more streamline shell given the same level of fire control.

The SV data is completely wrong for the whole table, which is easy to see since the first entry, at 500 yds, should be ~2400fps so each subsequent entry is considerably in error, and while TOF might be correct, it also might not be.

No one is claiming the same range for each gun. Max range for the pom-pom at 2300fps = 6800 yds. Max range for the Bofors at 2800fps is probably ~9-10,000 yds. However, max range is limited in both guns by the SD ammo to 3500 yds. The Bofors will be more accurate within that 3500 yd range but there are other factors as well. A quad pom-pom has a higher effective rate of fire than a twin bofors and thus there are more shells in the air to compensate for lower accuracy. In terms of TOF to 3500 yds, we have:

Bofors: 6.5 seconds (which may be incorrect)
1.1in: 8.1 seconds
20mm:13.3 seconds
pom-pom: ~8.5-9 seconds (my estimate for MV = 2300fps)

 

[Shortround6]

The SV data is completely wrong for the whole table, which is easy to see since the first entry, at 500 yds, should be ~2400fps so each subsequent entry is considerably in error, and while TOF might be correct, it also might not be.

And if you delete the 2800 fps entry and slide the rest of column up one line you get 2444fps. Not that far off your estimate is it?

That would make remaining velocity at 1000yds 2116fps compared to the 3in/50s 1000yd remaining velocity 2,345 fps. At least is sounds close.

No one is claiming the same range for each gun. Max range for the pom-pom at 2300fps = 6800 yds. Max range for the Bofors at 2800fps is probably ~9-10,000 yds. However, max range is limited in both guns by the SD ammo to 3500 yds.

I didn't say any one was claiming the same MAX range. And while you can adjust the tracer burn/self destruct to the same range it doesn't do anything for the time of flight.

The Bofors will be more accurate within that 3500 yd range but there are other factors as well. A quad pom-pom has a higher effective rate of fire than a twin bofors and thus there are more shells in the air to compensate for lower accuracy.

Ah, no. we have two aspects of accuracy here. More shells help with group dispersion, they help with the exact range estimation and the curve of the trajectory, they do not help if the mount is pointed several hundred feet away from where the target is.

In terms of TOF to 3500 yds, we have:

Bofors: 6.5 seconds (which may be incorrect)
1.1in: 8.1 seconds
20mm:13.3 seconds
pom-pom: ~8.5-9 seconds (my estimate for MV = 2300fps)

Even going by your estimate the target 300mph airplane is going to be 880ft further along it's flight path when the 2pdr shell gets there. It makes range measurement, speed measurement and course estimation much more critical. target is moving about 33% further at the same range. If you want comparable effectiveness you need the range the 2pdr can reach in 6.5 seconds.

With simple fire control the 40mm may have an effective range of only 1200yds which means the 2pdr is even shorter.

 

[RCAFson]

Ah, no. we have two aspects of accuracy here. More shells help with group dispersion, they help with the exact range estimation and the curve of the trajectory, they do not help if the mount is pointed several hundred feet away from where the target is.



Even going by your estimate the target 300mph airplane is going to be 880ft further along it's flight path when the 2pdr shell gets there. It makes range measurement, speed measurement and course estimation much more critical. target is moving about 33% further at the same range. If you want comparable effectiveness you need the range the 2pdr can reach in 6.5 seconds.

With simple fire control the 40mm may have an effective range of only 1200yds which means the 2pdr is even shorter.

Neither of these weapons have precision fire control (except the Hazemeyer Bofors and cruiser,BB, or CV mounted pom-poms with MK IV/type 282 radar control), and they rely on hitting by "hosing down" the target, so more rounds = better chance of hitting. If we accept a 33% reduction in accuracy for the pom-pom, it still means that a quad pom-pom will have about the same hit probability as a twin Bofors, at 3500 yds.

880ft = a crossing target on a perfect parallel course, but this number will decline as the target's path moves closer to an intercept course.

at 1200 yds the difference in TOF will be be very small, and here 4 barrells will certainly make a difference. The RN Pocket Gunnery book gives both an effective range of 1700 yds with "eye shooting".

 

[Glider]

Can anyone confirm that the US Destroyers did have directors for their 40mm guns, whereas the RN didn't?

 

[Wavelength]

^^USN light Flak had the excellent Stark Draper computing (optical) gun sight. This was an exclusive feature as far as I know.

Neither of these weapons have precision fire control (except the Hazemeyer Bofors and cruiser,BB, or CV mounted pom-poms with MK IV/type 282 radar control),

Type 282 radar wasn't very accurate or effective in practice, so it's not really a big plus having it over optical methods.

Much of problems of the BPF in dealing with Kamikaze had to do with their radar rather than guns. The British radar during this period was in state of disarray. The Skyatron system was a fiasco and the new centimetric radar system (277/293) supporting it demonstrated poor performance well into the 1950s. By using more primitive methods of command and control the old 3.3 meter Type 281 and particularly 7.5 meter Type 279 did prove valuable in the Pacific by virtue of their long range and pronounced vertical lobes structure.

The new 10cm firecontrol radars, Type 274 and Type 275, were having teething problems. Type 275 for Flak direction featured conical scan but proved very difficult to use in action. 50cm Type 285 was usually limited to ranging. Type 285M (which still predominated) had lobe switching but only on one axis so it had to be combined with optics.

Advanced light flak radar Type 262 was years away from operational deployment.

The Allied IFF system was a complete mess with only 40% of warships even equipped with IFF interrogators or transponders.

The USN was also having problems with radar, although this didn't affect their light flak. The Mk4 (FD) and its derivatives were demonstrating an inability to cope with Kamikaze and on destroyers especially were still hampered by being tied to an obsolete director with slow mechanical predictor. Naval equivalents to SCR-584 conical scan radar were not deployed because it was too big of a job to refit all the ships. The advanced Mk56 directors were not deployed and the make shift Mk57s did not reach the fleet until into 1945.

 

[RCAFson]

^^USN light Flak had the excellent Stark Draper computing (optical) gun sight. This was an exclusive feature as far as I know.



Type 282 radar wasn't very accurate or effective in practice, so it's not really a big plus having it over optical methods.

The Mk51/MK14 director was supplied to the RN, according to Campbell, and the RN developed an equivalent in the Simple Tachymetric Director, according to Campbell, however both these systems used a simple range estimation system, and could hardly be called precision systems - they only worked OK when there was a large volume of fire.

Regardless of how well Type 282/MK IV worked in practice, it was, theoretically, a precision system, where Mk 51 was not.