"What is a "heavy" naval AA gun?" Topic

I mean, in terms of a dedicated AA design; not a heavy gun that can be modified to fire AA, nor a dual-purpose 5" or a Japanese gun firing Beehives.

For example: a Bofors 40mm Quad? Is that "heavy" in traditional parlance?

40mm was considered "medium" at the time. I believe everything that was considered "heavy", say 3" and above, was dual purpose.

So I think that 40mm was about the "heaviest" dedicated AA gun, though it was a "medium". Confused yet?

I think the 5"/25 was pretty much a single-purpose AA gun, wasn't it? Definitely "heavy."

The Germans didn't have dual purpose naval guns. Their heavy AA was the 105mm (4.1")

link

3"and larger were considered heavy AA.
The Germans also had the 3.5"(88mm) Heavy AA.

In some cases larger guns were given a capacity for AA use, but the main purpose remained as surface engagement guns. The types used this way could be cruiser guns right up to the 18"beehive shells fired by Yamato and Musashi. They were for emergency use mostly and unable to track fast enough to be considered true AA guns.

Many medium sized heavy guns, were capable of use against surface or air targets and to be as good against either as the one. This can be confusing, but they are usually designated as DP or dual purpose.

AA Guns are considered in three categories.

HEAVY.
MEDIUM
LIGHT.

Heavy refers to guns of 3"and more.
Medium covers the 2pdr AA, 37mm and 40mm AA and various derivatives.
LIGHT covers 25mm, 20mm, right down to machineguns.

Until the arrival of the 40mm gun with the fleet, the British had a 'hole' in their AA cover. The heavy could work effectively out to certain ranges, but the 2pdr and smaller only at close range.
To cover the medium range gap, many destroyers were fitted with 3" or 12pdr guns, replacing one set of torpedo tubes. These guns proved pretty useless and were eventually replaced by 40mm.

Sorry if that is not entirely clear, but I am still recovering and writing under some difficulty.

I believe the Germans had a naval version of their 128mm AA gun developed for a class of DD's that were designed, but never completed.

The RN mounted not only 3" guns, but built 4 'L' class DDs with 8x4". Later in the war some of the Tribals gave up one 4.7" twin mount for a 4"twin mount. The KGV BB's had a secondary armament utilizing 5.25" guns. The gap Mal describes cost the RN a lot of ships.

After the war the USN completed two Worchester class CLAA's with a combination of 6" DP & 3" DP. It would have been interesting to see how they would have handled the Kamikaze threat.

I think Mal, has pretty much broke down the categories as I have seen it referred to in most reference books.

Thanks; this is interesting and provides some degree of quandary with regard to thinking about the representation of AA guns in games. Since planes fly so much faster than ships move, I wonder if it makes any sense to try to break this down into different processes, or if it's simply a case that each ship is throwing up X-amount of AA firepower, all-told.

Do it by ranges; close, medium and long.

close, medium and long.

Exactly what I use for my convoy games. Anything else is micro management that slows things down for no real value.

German- 105mm or 4.1" as found on Bismarck.

British- 5.25" really was a DP, although later destroyer guns were 4.5" based mostly on AA experience.
The 4", especially the twin, was a near exclusive AA mount, although it was a shell heavy enough to go through a uboat hull casing too.

Japan did have a 5" fire HA fire like the US. Sometimes found on unmodified ships or even late war escorts. Japan also had an incredible 3.9" on late war destroyers, although it was DP but based on good AA performance.

Italy, I think 90mm on the Littorios'.
France, like Italy I believe in the 85-90mm range.

Surprisingly…the 4"AA. Single or twin mount, could not penetrate a U Boat hull. The outer casing yes, but not the inner hull. Thus the British developed the 'SHARK' shell which could do the job, but appeared far too late and the only recorded uses were after the war when sinking U Boats during tests.

Only shells of 4.7"and larger (the later 4.5" was an exception) could penetrate a U Boat hull. But even then penetration of a round, extra strength steel object could be difficult for most shell types. Even those expected to penetrate could easily glance off unless it struck at just the right angle.

The 4"AA was however an excellent AA weapon and with its rapid fire could also deliver a lot of shells onto a target within a short time.

3" and 12pdr British AA guns were mostly old. While reasonable for WW1 they were out of place in WW2 mostly because they lacked the tracking and range finding facilities needed. It has been said that their main function was to give Destroyer crews the feeling that they were doing something, rather than sitting helplessly under air attack.

The 8"guns of British County Class cruisers could be used in the AA role but like most larger weapons could only take part in barrage fire. They did not aim for a specific target. At Leyte Gulf, on one occasion the Australian Cruiser HMAS Australia fired at night, using full flash powder. Next day 'Tokyo Rose' accused them of using ineffective flame throwers against attacking aircraft!

The IJN Takao class CA's following the RN example on the Kent class, gave their 8" turrets a 70 degree elevation. However, due to the light weight of the elevating & recoil mechanism, effective max. elevation was 55 degrees. But, I don't remember any mention of them being used in the AA role.
Reference: 'The Heavy Cruiser Takao' by Janusz Skulski.

I believe the 9-152mm guns on the French Richelieu class were also considered to be dual purpose guns. But I believe the mountings were overly complicated and the guns did not work well in the DP mode.

That is correct re the Richelieu. The designers were asked to do too much, but were also hampered by having to keep too many things common with guns already in use. That prevented them adding new features. But worst of all was that they were really designed around early 1930's technology when aircraft capabilities were way below that of WW2. Consequently the guns would have been great if aircraft performance had remained the same as 1930, but of course by 1939-40 was much more advanced.

The biggest difficulty for heavy AA guns is the ability to track a fast moving target. Hence barrage fire was normally used to provide an area of bursting flak that the aircraft had to fly through. But the second difficulty was that unless the range finding and directing equipment was very capable, it was difficult to keep the barrage area moving sufficiently ahead of the targets for the zone to be a continuing threat.

Even in WW1 it was found that the time in which to get accurate bearings on an oncoming aircraft and then fire in time for the bearings to still be accurate, was very small.
Mere seconds. By WW2 it was even harder.

When the USN went to Radar Fire control for their AA and to using proximity fuses this was a quantum leap in AA effectiveness. Of course I believe the USN also had a very effective AA director too. Has anyone seen any estimates on how much more effective AA fire was when these two advances were made?