Rn vs IJN (2 Viewers)

[Glider]

Comparing some IJN vs RN destroyer classes
IJN
Fubuki (1928 - 24 built) 6 x 5" guns, 9 x torpedo tubes, 18 x torpedoes, 18 x depth charges, 38 knots
Akatsuki (1932 - 4 built) 6 x 5" guns, 9 x Torpedo tubes, 18 x torpedoes, 18 x depth charges, 38 knots
Hatsuharu (1931 - 6 built) 4 x 5" guns, 6 x torpedo tubes, 18 x depth charges, 36 knots
Shiratsuyu - (1933 - 10 built), 5 x 5" guns, 8 x torpedo tubes, 16 x torpedoes, 16 x depth charges, 33 knots
Asashio - (1937 - 10 built), 6 x 5" guns, 8 x torpedo tubes, 16 x torpedoes, 36 x depth charges, 35 knots
Kagero - (1939 - 19 built), 6 x 5" guns, 8 x torpedo tubes, 16 x torpedoes, 36 x depth charges 35.5 knots

RN
A-Class (1924 - 20 built) 4 x 4.7" guns, 8 x torpedo tubes, 35 knots
D-Class (1930 - 20 built) 4 x 4.7" guns, 8 x torpedo tubes, 20 depth charges, 36 knots
H-Class 1934 - 24 built) 4 x 4.7" guns, 8 x torpedo tubes, 20 x depth charges, 35.5 knots
Tribal Class (1938 - 27 built) 8 x 4.7" guns, 4 x torpedo tubes, 20 x depth charges, 36 knots
J-K-N Classes (1937 - 24 built) 6 x 4.7" guns, 8 x torpedo tubes, 2 launchers for dc, 36 knots

Overall, on balance, it looks to me like the IJN destroyers are a bit more heavily armed, though it is pretty close. But of course, the IJN torpedoes are faster and have a good bit better range.

A couple of small points.

a) The LM Class are missing from your list I think 16 built

b) The numbers. Japanese Destroyers 73 built, RN Destroyers 131 built (including LM)

 

[Shortround6]

By late 1941 a lot of British destroyers had traded one set of TTs for a not very effective AA gun.
By late 1941 a lot of British destroyers were carrying a lot more depth charges that what they carried in the mid or late 30s.
In 1941 some (maybe not a lot) of British destroyers were starting to get a few 20mm guns.
From the Tribal's on the British destroyers had a quad 2pdr AA gun.

Granted it was only one per ship but the Japanese destroyers had???
Asashio as built had two of these, one on each side of the funnel.

They fired almost twice as fast as the British gun did but since they used 15 round magazines stuck in the top compared to the 112 round belts in the 2pdr, effective rate of fire during an attack??????British could hook in 14 round belts together so they didn't have to wait for the belt box to be empty.

I would also note that according to one source the Asashio as built carried 16 depth chargers, not 36.
When they got 36 depth charges they gave up one set of torpedo reloads.
By the time they got to 28 of the 25mm guns they had given up one of the twin 5in turrets.

Edit. The Asashio's were the first Japanese destroyers to get the 25mm guns as built.
The Earlier classes had two, count them TWO, 13mm Hotchkiss guns.

Note the 30 round magazine. Ran dry in about 4 seconds.
Some ships were upgraded a bit before 1942 but any substantial increase in aa guns called for a main turret to be take out.

 

[Shortround6]

Most British Destroyers before the Tribals had these

One on each side of the ship. Now in actual effect these were crap, Which means the Japanese (and French and Italian) 13mm Hotchkiss guns were worse than crap.
Some of the old British destroyers had these.

these used lower velocity ammo than the 2pdr multiple mount guns and often canvas belts.
But around 100rpm beats the heck out of the before/early war German 37mm AA guns which were NOT automatic.

A lot of the Tribal class, if they lived long enough, had X 4.7in mount removed and replaced by a twin 4in mount which sort of shows what they thought of the 4.7 as an AA weapon despite pre war planning. A four of the Canadian Tribals (1943 on) were built with eight 4in guns.

Tribals got 30 depth charges pretty much to start (war load) and wound up with up to 46. By the end of the war most had 2 40mm Bofors and/or 8-12 20mm guns added.

British ships were built with a bit more stability to begin with, usually (there were some exceptions). Weapon shortages really affected refits as they were trying to arm hundreds of smaller escorts and merchant ships at the same time.

 

[Glider]

Lets not forget that most of the USN destroyers started with a handful (4 to 12) 0.5 machine guns and were no better than any other navy.

 

[Shortround6]

Lets not forget that most of the USN destroyers started with a handful (4 to 12) 0.5 machine guns and were no better than any other navy.

Quite true, and 12 machine guns would have been rare indeed.

But because they were water cooled and belt fed.

I personally rate them as crap instead of below crap like the 13mm Hotchkiss and clones

 

[Wild_Bill_Kelso]

Regardless, nobody had AA good enough to stop or really seriously harm strike aircraft units sufficiently until a year or two into the Pacific War.

The US ships with the 5" / 38, Oerlikon 20mm and later Bofors 40mm were fairly well armed. But that didn't make them safe from dive bombers and torpedo bombers.

The lesson learned was that AA, even really good AA like you had on 1943 vintage US light Cruisers, wasn't really enough to save a ship without air superiority.

 

[Shortround6]

Regardless, nobody had AA good enough to stop or really seriously harm strike aircraft units sufficiently until a year or two into the Pacific War.

I am not sure what you mean by "strike aircraft units".

You are correct if you mean seriously harm a squadron or several squadrons of aircraft in one strike.
Stopping such a group was possible and was done. Stopping meaning prevent them from inflecting damage for an hour or two on one day.
Obviously individual aircraft could be shot down or seriously damaged but that is not enough to take out or cripple the unit.

It is not black or white. There are a lot of shades of grey. From darn near charcoal to off white.

Small ships, like destroyers, are seldom targeted (unless misidentified) by aircraft in large actions as there are higher value targets around. With few or no large targets Destroyers can take a pounding. And then it starts getting into luck. Skill of each pilot, skill of a gunner, bent fin on a bomb, random butterfly. Germans dropped a lot of bombs on ships at Dunkerque, they got some, not all. They dropped a lot on Malta convoy's. They got quite a number of ships but not all, over a period of months. Germans and Italians attacked a lot of ships around Crete, sank a number, but not all and sometimes not until the 2nd or 3rd day.
Better AA might not kill a single plane, it may damage a few, (those G3Ms got shot up pretty well attacking the PoW and Repulse and the Repulse had one of the worst heavy AA batteries of any major (larger than destroyer) unit in the British fleet.) What AA can do is cause planes to drop from higher or further away, which increases chances of missing, does not guarantee a miss.
If an AA battery defends a target and does not shoot down one plane but the target is not hit, does the AA battery consider that a success or not?
If the AA Battery shoots down 4-6 planes but the target is hit is that a failure? Battery failed to defend the target?

Bombers/strike aircraft can return another day and repeat the attack/s. Successful defense one day is not a guarantee of success the next day.

British destroyers were, on average, smaller than the Japanese Destroyers. It varied somewhat by class and the classes varied in size and not according chronology. British did have a lot more. More to start and more as the war went on.
Japan launched and completed 33 fleet Destroyers from the start of 1941 to the end of the war.
Britain (and Commonwealth) launched 101 Fleet Destroyers from the start of 1941 until the end of 1943. They launched another 34 in 1944, I don't know how many of those were completed before the war ended.

British (and C) built 86 Hunts, all launched before the end of 1942.
Japan built 15 Matsu's all launched in 1944 and 14 Tachibana's, all launched in 1944 and 45.

The Japanese have to sink ships at a higher rate than the British do. The British have time and numbers on their side. The Japanese do not. And Japan does not have a technological edge on average.

 

[EwenS]

The last of the destroyers ordered under the 1941 Programme were the .Ca flotilla, the last of which completed in Feb 1945.

The 1942 Programme included 2 flotillas (16 ships) of the big new Battle class plus 3 flotillas (24 ships) of C class, the Ch/Co/Cr flotillas. The common feature of these ships was a new director tower, the Mk.VI. Production of these was delayed and completion of these classes had to be slowed pending delivery. Barfleur, the first Battle, completed in Sept 1944 without its director, which was finally fitted in Nov 1944.so that trials of the system could begin. She was the only vessel of these 40 ships to see war service, reaching the Pacific to join the BPF off Japan in July 1945.

Only another 4 Battles and the first of the C class completed by 15 Aug 1945. However by the end of 1945, another another 3 Battles and 14 C class had joined the fleet.

The additional topweight from the new director meant the sacrifice of one set of torpedo tubes in the 3 C flotillas, and some adjustments to the light AA.

All the Hunt class were built in Britain, as were the first 4 Canadian Tribals. The second group of 4 were built in Canada but neither of the 2 wartime launches was completed in time to see war service. The 3 Australian Tribals were built there, and were the only British designed destroyers to see wartime service built outside Britain. No war in Europe in 1939 means no Hunt class, while fleet destroyer designs continue to grow in size to tackle Japanee ships as discussed before.

In terms of light AA, the Tribals and later classes were designed not only with a quad pom pom but also a pair of quad 0.5"

In 1937 the RN began looking for a new light AA weapon. In 1938 they rejected the Oerlikon 1934 20mm design but encouraged the company to raise its muzzle velocity and simplify its design for ease of operation by non-specialist personnel. That design was accepted in 1939 and a large order placed with Oerlikon in Switzerland. But then France fell before many could be delivered (Only about 100 or so). Britain also acquired a licence to produce them in the UK but poblems of wartime in acquiring the necesary labour and machine tools meant production guns didn't start to appear until autumn 1941.

So, no war in Europe, those Swiss deliveries continue and more Oerlikons are at sea in 1941 and maybe British production happens earlier.

Britain also showed interest in the 40mm Bofors in the 1930s, but the priority was for the British Army, with orders being placed in 1937. Again a licence to produce was obtained, as it was by half of Europe, with production starting slowly in 1939.

 

[Wild_Bill_Kelso]

I am not sure what you mean by "strike aircraft units".

What I mean more precisely is this:

In terms of the 'white to gray to black' - AA can 1) have no effect 2) dissuade enemy aircraft from attacking effectively 3) destroy one or two and damage 2 or 3 out of a unit (squadron or equivalent) so incrementally degrade the unit 4) destroy and damage enough aircraft to either substantially degrade (50% or more) the unit / and / or drive them away / disrupt the attack 5) destroy the unit (90% losses or more).

Anything below 4 is not really a success, IMO.

You mentioned 'revenge weapons' - AA in WW2 often played this role in the sense that while it was pretty rare to actually stop an air raid with the AA guns alone, it was possible to destroy or degrade a unit sufficiently (i.e. category 4 above) that there would either be a delay in their returning to attack again, and / or with severely degraded capability for their next and subsequent attacks.

Once you get to ships like a mid 1943 era Atlanta class CL, ala the USS Oakland, or the equivalent in firepower from multiple ships, it was possible to completely or substantially destroy enemy air units attempting to attack. Oakland had the following armament (per Wikipedia):

• 12 × 5 in (127 mm)/38 caliber Mark 12 guns (6×2)
• 4 × quad 40 mm (1.6 in) Bofors anti-aircraft guns
• 4 × twin 40 mm (1.6 in) Bofors anti-aircraft guns
• 16 × 20 mm (0.79 in) Oerlikon anti-aircraft cannons

Even a lesser group of US destroyers, with the 5" /38 guns, often inflicted sufficient damage on attacking aircraft that within 1-3 missions they would be 'degraded' to the point that they could no longer make attacks. And sometimes they achieved 'category 5' i.e. substantially destroyed attacking units, even in 1942.

The problem was that some aircraft like the SBD, Ju-87, D3A, B5N, and G4M turned out to be able to get hits and sink ships at a fairly high rate. A squadron of 8-12 aircraft was fairly likely to hit and seriously damage or sink a ship. Even if you fairly well wrecked the attacking squadron you may still lose one of your warships. Which isn't a good trade.

I don't think the RN had the equivalent of the 5" / 38 guns on their ships.

If the AA could not drive the enemy raid away, the next best thing was to degrade it. But until you had the equivalent of the armament listed above, chances of stopping a raid through shipborne AA alone were pretty low.

You are correct if you mean seriously harm a squadron or several squadrons of aircraft in one strike.
Stopping such a group was possible and was done. Stopping meaning prevent them from inflecting damage for an hour or two on one day.

I think that was pretty rare

Obviously individual aircraft could be shot down or seriously damaged but that is not enough to take out or cripple the unit.

It is not black or white. There are a lot of shades of grey. From darn near charcoal to off white.

Agreed, it's definitely a range especially with AA

Small ships, like destroyers, are seldom targeted (unless misidentified) by aircraft in large actions as there are higher value targets around.

I think one of the mistaken pre-war assumptions was that there would always be higher value targets around (ala the big fleet battles that never really happened), that was not always the case.

With few or no large targets Destroyers can take a pounding. And then it starts getting into luck. Skill of each pilot, skill of a gunner, bent fin on a bomb, random butterfly. Germans dropped a lot of bombs on ships at Dunkerque, they got some, not all. They dropped a lot on Malta convoy's. They got quite a number of ships but not all, over a period of months. Germans and Italians attacked a lot of ships around Crete, sank a number, but not all and sometimes not until the 2nd or 3rd day.

Destroyers in the Pacific, on both sides, tended to be pretty hard to hit from the air, due to their agility and various countermeasures (including smoke etc.). Though they were sometimes hit and sunk.

Better AA might not kill a single plane, it may damage a few, (those G3Ms got shot up pretty well attacking the PoW and Repulse and the Repulse had one of the worst heavy AA batteries of any major (larger than destroyer) unit in the British fleet.)

Wikipedia shows 4 aircraft destroyed, 28 damaged. One G3M and two G4M were destroyed, with a third badly damaged that crashed while landing. That's a good trade for 2 capital ships.

Prince of Wales was apparently fatally damaged by the first single torpedo hit, though she was hit by three more torpedoes and one bomb. Repulse was also hit by four torpedoes and sank within six minutes.

What AA can do is cause planes to drop from higher or further away, which increases chances of missing, does not guarantee a miss.
If an AA battery defends a target and does not shoot down one plane but the target is not hit, does the AA battery consider that a success or not?
If the AA Battery shoots down 4-6 planes but the target is hit is that a failure? Battery failed to defend the target?

Per above, if the AA forces the air strike to abort, I'd say it's definitely a successful mission. Second best would be to rattle them so much that they all miss. That seems to have been one of the hardest goals to achieve though. Tertiary would be to damage the striking unit so that they can't maintain operations, or have to pause for a while. Also pretty hard.

Bombers/strike aircraft can return another day and repeat the attack/s. Successful defense one day is not a guarantee of success the next day.

Right, if they are not sufficiently degraded.

British destroyers were, on average, smaller than the Japanese Destroyers. It varied somewhat by class and the classes varied in size and not according chronology. British did have a lot more. More to start and more as the war went on.
Japan launched and completed 33 fleet Destroyers from the start of 1941 to the end of the war.
Britain (and Commonwealth) launched 101 Fleet Destroyers from the start of 1941 until the end of 1943. They launched another 34 in 1944, I don't know how many of those were completed before the war ended.

British (and C) built 86 Hunts, all launched before the end of 1942.
Japan built 15 Matsu's all launched in 1944 and 14 Tachibana's, all launched in 1944 and 45.

The Japanese have to sink ships at a higher rate than the British do. The British have time and numbers on their side. The Japanese do not. And Japan does not have a technological edge on average.

Japanese production may have also been impacted by all the trouble they had fighting the Americans, the need to replace aircraft carriers, interruptions in supply lines etc. I don't think we can assume to much past the first year or two of the war.

I don't think it's true to say that Japan doesn't have a technological edge on average. In some areas they certainly did - the torpedo, the optics, they seem to have had bigger guns on a lot of their ships.

Probably the training and discipline too, though that is not technological, it leverages the technological advantages they did have such as for night surface combat.

 

[EwenS]

Once you get to ships like a mid 1943 era Atlanta class CL, ala the USS Oakland, or the equivalent in firepower from multiple ships, it was possible to completely or substantially destroy enemy air units attempting to attack. Oakland had the following armament (per Wikipedia):

• 12 × 5 in (127 mm)/38 caliber Mark 12 guns (6×2)
• 4 × quad 40 mm (1.6 in) Bofors anti-aircraft guns
• 4 × twin 40 mm (1.6 in) Bofors anti-aircraft guns
• 16 × 20 mm (0.79 in) Oerlikon anti-aircraft cannons

Note quite. You picked the AA armament after her 1945 refit not as completed in 1943.

As completed 1943-45 the weapon fit in these 4 ships was:-

• 12 × 5 in (127 mm)/38 caliber Mark 12 guns (6×2)
• 8 × twin 40 mm (1.6 in) Bofors anti-aircraft guns
• 16 × 20 mm (0.79 in) Oerlikon anti-aircraft cannons (16x1)
• 8x21" TT (2x4)

Then in 1945 the refits began with a view to increasing the AA firepower. In April 1945 Oakland had been upgraded to:-

• 12 × 5 in (127 mm)/38 caliber Mark 12 guns (6×2)
• 4 × quad 40 mm (1.6 in) Bofors anti-aircraft guns
• 4 × twin 40 mm (1.6 in) Bofors anti-aircraft guns
• 16 × 20 mm (0.79 in) Oerlikon anti-aircraft cannons (in 8 twin mounts)

These ships were exceedingly weight critical. So the TT had to removed as weight compensation for the extra AA armament. Reno followed when she completed her repairs in Oct 1945. Tuscon also lost her TT before the end of the war, but without the AA upgrade. Flint kept her original fit.

 

[Wild_Bill_Kelso]

Fair enough, I guess I missed that on the Wiki - I think the AA armament per the 1943 refit is plenty though, and in fact many of the Atlanta class were refitted with more AA guns in late 1942.

On 20 November 1943, when their task force near the Gilbert Islands was attacked at twilight by a large force of G4M torpedo bombers, the USS Oakland got permission to activate their running lights and turn themselves into the main target, and they succeeded in destroying 2 aircraft and disrupting the attack, taking no hits. I'd call that a 'level 4 success'

 

[RCAFson]

Fair enough, I guess I missed that on the Wiki - I think the AA armament per the 1943 refit is plenty though, and in fact many of the Atlanta class were refitted with more AA guns in late 1942.

On 20 November 1943, when their task force near the Gilbert Islands was attacked at twilight by a large force of G4M torpedo bombers, the USS Oakland got permission to activate their running lights and turn themselves into the main target, and they succeeded in destroying 2 aircraft and disrupting the attack, taking no hits. I'd call that a 'level 4 success'

The USN was using VT ammo after Jan 1943.

 

[Shortround6]

I would note that the 4 Atlanta's were designed with

8 × dual 5"/38 caliber guns
4 × quad 1.1"/75 caliber guns
6 × single Oerlikon 20 mm cannons
2 × quad Mark 15 torpedo torpedo tubes

The Oakland and later lost the waist dual 5"/38 on each side in favor of more light AA. Without proximity fuses for the 5"/38 the new medium (Bofors guns) AA was actually more effective.
The San Diego fought in the Pacific from June of 1942 (just missed Midway) to Dec 1943 when she to San Francisco for new radar, a combat information center and replacement of her quad 1.1in guns with 40mm Bofors guns. She ended the war with four quad 40mm but I don't know if she go them in the Dec 43 refit or if she only got twins at that time (?).

Radar and gun directors made considerable changes in WW II. By 1945 many quad (and some twin) 40mms had individual fire control radars fitted for each mount. Each mount having it's own gun Directors.

The Atlanta class could not make full use of their eight twin turrets (later six) because they didn't have enough gun directors to engage multiple targets. As built they only had two high angle directors.
This was a major problem with many late 30s and early 40s ships. The Bismarck only had 4 high angle directors and so could only engage a max of 4 separate aircraft at time and they had to approach from the right angles. Only two directors faced each side of the ship. All ships could be overwhelmed by enough airplanes to exceed the fire control capacity.

 

[Shortround6]

A lot of the US 1930s destroyers were built with four .50 cal guns. Many of them were modified to have eight .50s in the summer of 1941 as noted by one of our contributors earlier. However there was a lot of stuff taken off the ships as partial compensation, They also got more Depth charges at the same time.
Some of them got a few 20mm guns instead of the full eight .50s. for a mixed battery to start.
The Sims class introduced the MK 37 Director but the class was overweight for a number of reasons and they lost one set of tubes and one 5in gun during 1941 to make up for more depth charges and throwers.

The RN was trying to upgrade ships even in the early part of the war but limited production was a problem.
In most accounts the Japanese didn't really upgrade until 1942 or early 1943?
Japanese often pulled a turret cutting the ships to to four 5in guns in order to mount more 25mm AA guns in 1943-44.

In some cases it seems like some of the AA guns were fitted to some of these ships for morale purposes rather than the expectation they were going to do anything. British did a lot of this, a single 4in gun with no real fire control had a vanishingly small chance of actually hitting anything.

 

[Wild_Bill_Kelso]

I would note that the 4 Atlanta's were designed with

8 × dual 5"/38 caliber guns
4 × quad 1.1"/75 caliber guns
6 × single Oerlikon 20 mm cannons
2 × quad Mark 15 torpedo torpedo tubes

The Oakland and later lost the waist dual 5"/38 on each side in favor of more light AA. Without proximity fuses for the 5"/38 the new medium (Bofors guns) AA was actually more effective.
The San Diego fought in the Pacific from June of 1942 (just missed Midway) to Dec 1943 when she to San Francisco for new radar, a combat information center and replacement of her quad 1.1in guns with 40mm Bofors guns. She ended the war with four quad 40mm but I don't know if she go them in the Dec 43 refit or if she only got twins at that time (?).

Radar and gun directors made considerable changes in WW II. By 1945 many quad (and some twin) 40mms had individual fire control radars fitted for each mount. Each mount having it's own gun Directors.

The Atlanta class could not make full use of their eight twin turrets (later six) because they didn't have enough gun directors to engage multiple targets. As built they only had two high angle directors.
This was a major problem with many late 30s and early 40s ships. The Bismarck only had 4 high angle directors and so could only engage a max of 4 separate aircraft at time and they had to approach from the right angles. Only two directors faced each side of the ship. All ships could be overwhelmed by enough airplanes to exceed the fire control capacity.

16 x 5" / 38 guns is pretty good for early 1942. You may not like those 27mm but 16 of them don't hurt, and Wiki says 8 x 20mm cannons as well. Also notes SC air search radar in 1942. They apparently had surface search too and used in at the Naval Battle of Guadalcanal in Nov 1942, before being mortally crippled by a torpedo and friendly fire from the San Francisco.

 

[WARSPITER]

The RN started to get it's first VT ammo for the 4.5" AA on carriers from September 1943.

 

[z42]

I don't think the RN had the equivalent of the 5" / 38 guns on their ships.

What do you mean? The 5"/38 was perhaps the gold standard, but AFAIU (some) of the RN guns were pretty good too. Their problem was perhaps more that they were spoiled for choice, with 4", 4.5", 4.7", and 5.25" guns in this size class. Some of these were maybe not excellent, but apparently they were pretty happy with the 4.5", and it became the standard RN gun in the post war era.

 

[Shortround6]

The 5in/38 was the gold standard because of it's rate of fire, which was rather dependent on the mount.
It's slightly shorter barrel helped with training and elevation compared to most contemporaries.
The 5.25" was not really a good AA gun. It may not have been bad but it had too many compromises for anti-destroyer surface fire.
The 4.7" was sort of a mess seeing as how there were 3 different guns and ammo set ups.
The 4.5" was pretty good but there were some mount issues.
The 4" was pretty good. It was considered too light for surface work but in actual combat it seems to have worked pretty well against ships.

Part of the problem in comparing these shows up real quick in the weights.
A twin 5.25" mount went 78-96 tons and needed quite a bit of structure underneath it.
A Twin 4" mount went about 19 tons, not quite a bolt to the deck but it didn't require the amount of structure underneath it.
The 4in could fire almost twice as fast as the 5.25" but the shells were just under 1/2 the weight. The 4" was shorter ranged but in smaller hulls the long range was something of an illusion.
Rolling, pitching hulls degrade practical accuracy quite a bit even in anything but a dead calm.

The US 5"/38 was the gold standard also because just about all the different mounts allowed for 85 degrees of elevation which meant that even in 1935 the US destroyers were getting guns that could point almost straight up. Effective fire control may be different story although they got DP director even in the 1934-35 Farraguts.

The Japanese 5"/50s in the Fubuki's and and later show the difference between nominal dual purpose guns and actual dual purpose guns. The Early Fubuki's had guns that could elevate to 40 degrees which is actually pretty good for the late 20s. The later Fubuki's could elevate 70 degrees which justifies the dual purpose title, however the gun mounts turned slow, the bag chargers meant they had to be lowered to 10 degrees to reload, they used manual ramming, and they were not given AA directors.
Some (few) of the Japanese destroyers in WW II had one of the twin 5"/50 mounts taken off and replaced by a twin 5"/40 mount to improve AA fire which sort of tells you something.

 

[RCAFson]

The 5in/38 was the gold standard because of it's rate of fire, which was rather dependent on the mount.
It's slightly shorter barrel helped with training and elevation compared to most contemporaries.
The 5.25" was not really a good AA gun. It may not have been bad but it had too many compromises for anti-destroyer surface fire.
The 4.7" was sort of a mess seeing as how there were 3 different guns and ammo set ups.
The 4.5" was pretty good but there were some mount issues.
The 4" was pretty good. It was considered too light for surface work but in actual combat it seems to have worked pretty well against ships.

Part of the problem in comparing these shows up real quick in the weights.
A twin 5.25" mount went 78-96 tons and needed quite a bit of structure underneath it.
A Twin 4" mount went about 19 tons, not quite a bolt to the deck but it didn't require the amount of structure underneath it.
The 4in could fire almost twice as fast as the 5.25" but the shells were just under 1/2 the weight. The 4" was shorter ranged but in smaller hulls the long range was something of an illusion.
Rolling, pitching hulls degrade practical accuracy quite a bit even in anything but a dead calm.

The US 5"/38 was the gold standard also because just about all the different mounts allowed for 85 degrees of elevation which meant that even in 1935 the US destroyers were getting guns that could point almost straight up. Effective fire control may be different story although they got DP director even in the 1934-35 Farraguts.

The Japanese 5"/50s in the Fubuki's and and later show the difference between nominal dual purpose guns and actual dual purpose guns. The Early Fubuki's had guns that could elevate to 40 degrees which is actually pretty good for the late 20s. The later Fubuki's could elevate 70 degrees which justifies the dual purpose title, however the gun mounts turned slow, the bag chargers meant they had to be lowered to 10 degrees to reload, they used manual ramming, and they were not given AA directors.
Some (few) of the Japanese destroyers in WW II had one of the twin 5"/50 mounts taken off and replaced by a twin 5"/40 mount to improve AA fire which sort of tells you something.

If you read Lundstrom's 3 volumes on the 1942 airwar (First Team and Black Shoe...) in the Pacific, you'll note that he assessed the 5in/38 as ineffective as an AA weapon. Medium calibre AA, without VT ammo was just too inaccurate, for a variety of reasons. to be of much use against aircraft. It did have a deterrent value, though.

OTOH, the USN BuOrd claimed massive numbers of AA kills in 1942 including many 5in/38 kills but the vast majority of these claims cannot be verified via IJN records.

 

[Wild_Bill_Kelso]

When we went through all the air / sea battles in the Pacific, including I think upthread in this thread, you can see several raids in which the Japanese strike groups were decimated by the USN AAA. Including in 1942.