So for a Tribal class with 8 x 4.7in we have 26sec x 8 guns = 34.7 shots
and for a JKM class, 26 sec x 6 guns = 26 shots
(assuming 10 RPM/gun)
A Benson or other 4 gun USN destroyer (typical prewar) we have 34 sec x 4 guns = 27 shots
(assuming 12RPM/Gun, the RoF according to Crenshaw of USS Maury )
later class with 4 guns = 34 rounds
(Later USN destroyers had a higher rate of fire, due to a superior fuze setter arrangement and had a RoF of 15RPM/gun)
Its not a fair comparison. you are comparing the theoretical rof of the british DDs with the practical rof for the bensons. The two terms are not interchaneable. The practical rof for the 4.7in was around 4-8 rpm. On that basis the Tribals will get off around 13-14 rounds (from an 8 gun broadside) , whilst the JKN will be propportionally smaller. If you want to compare theoretical maximums, you need to do so for all classes, In that case the rofs are 10rpm for the 4.7 and 24 rpm for the 5/38, which we could arbitarily taken as 20rpm, simply because some sources say its 20rpm. On that basis, the Bensons will get off 54 rounds in the same time as the 13 rounds are fired by by the tribals and about 10 for the JKNs. There is simply no comparison in the ROFs.
Ive served on ships that have the 4.5in as main armament, and observed fire onboard Gearing class DDs. I can assure you there is no comparison when it comes to Practical rofs. I will concede that in reality the theoretical rofs are not a true reflection of actual practical rofs. the po st war 5/54 with auto loader has a theoretical rof of nearly 60 rpm, but in reality could only sustain about 20 rpm. Hand loaded mounts will never do well when it comes to actual sustained rof, and rammed breeches are even worse when the mount is operating in the AA role.
This is moreso the case for the 4.7 guns, which still required ramming of each round. at elevation the workable rate of fire would have dropped right away, as crews struggled to get each round rammed home and in the chamber. Trying to argue that the British DDs had a comparable ROF to the bensons in an AA role is a complete dud Im afraid.
The RN destroyers will also be able to engage the aircraft with their quad pom-pom. Overall I don't see a huge
advantage for the USN destroyers, and if we include the pom-pom, I'd say they were at a disadvantage, because their CIWS = 4 x .5in HMGs.
Only the 2pdrs can provide any real fire against torpedo bombers, and that is a theoretical capability, not a real one. 20mm weapons and MGs were almost totally impotent against torps fired at normal ranges because they lacked sufficient effective range. They were effective at making torps keep their distance, that i will grant you.
The 2 pdr was judged an advanced weapon when introduced, but by the outbreak of World War II advances in aircraft would have made it obsolete but for the introduction of a high-velocity round and new director designs (which were not available at the beginning of the war for DDs) . It was intended that the curtain of fire it threw up would be sufficient to deter attacking aircraft, which it could sometimes achieve, but its performance was hampered by the ineffective Mk III director.The MK IV Director with a Gyro Rate Unit and Type 282 radar was an improvement and was introduced on the King George V-class battleships, but not in DDs until much later.
In January 1941, HMS Illustrious′s Mk VIII mountings performed flawlessly firing 30,000 rounds with very few stoppages (accounting for 2 known kills). When HMS Prince of Wales was attacked and sunk by Japanese aircraft near Singapore, the subsequent RN report judged that a single 40 mm Bofors gun firing tracer was a more effective anti-aircraft weapon than a full eight barrelled pom pom. The Bofors had better range (about double in terms of effective range) and could deliver far more accurate fire, compared to a multiple pom-pom in director control, as the pom-poms did not have tracer ammunition, and the weapon lacked effective range. In the PoWs case, moreover, the pom-pom ammunition had deteriorated badly in their ready use lockers, while the Type 282 radar units also failed in the equatorial heat. In the same action, the Commissioned Gunner of HMS Repulse spent the whole action running from one pom-pom mount to another trying to keep them operational due to the faulty ammunition. The pom-poms on Repulse shot down two of the four confirmed kills made by Force Z, while Prince of Wales′ pom-poms did record hits on enemy aircraft but no kills (the other 2 of the total 4 losses were not lost to british action) . The Royal Navy judged the pom-pom's effectiveness to range from about half that of the Bofors, per gun, against torpedo planes to about equal against Kamikaze attackers. This was because Kamikazes had to penetrate to within the kill zone of the weapon more than anything
So no, against a torpedo bomber operating at normal range, I would say the CIWs aboard the British ships would make hardlky any difference. They made some difference to Divebombers and Suicide aircraft, but if a D/B or Kamikaze is that close, as to allow the pom poms to be effective, the Pom Pom has failed in its primary deterrent role anyway. 30000 rounds to shoot down 2 aircraft is not a great result, and not evidence of an effective weapon. Compare that to the 14-26 confirmed kills (depending on who you read) from the South Dakota a year or so later at Santa Cruz, and you start to get some idea of the different efficieny levels of the two weapon systems.
The other factor is the time for the AA FC computer to generate a solution. Crenshaw says it took about 30 seconds for the Mk 33 computer. My understanding is that the FKC could come to solution very quickly and RN picked FKC and HACS to avoid the slow solution speeds of tachymetric computers as used on USN destroyers.
Thats completely at odds with both campbell and Nav Weapons. this will get down to who you want to believe.....I choose to believe Campbell and Nav weapons. And operational results that we do have, whilst pretty sparse, dont support the claims you make in this regard.