Just a quick example on how tricky it is to assess technology and hardware optimums. I'll use a Second World War example, for it's so obviously low-tech by today's standards which makes the point (hopefully) more convincing.
Let's look att he optimal air defence armament of surface warships in the 1930's and 1940's period.
The legacy equipment from the 1920's was largely about guns calibre 75 mm to 90 mm, often with rather modest (light field gun-like) muzzle velocities. These guns were originally (pre-WW1) meant to chase away if not destroy dirigible airships. There were also some machineguns, of course.
More powerful anti-air weaponry was very rare during the 1920's.
The 1930's began, pre-1918 ships were increasingly replaced with new designs and there was a greater diversity:
(a) Very light anti-air wepaons of 12.7 to 20 mm calibre (HE shells for 20 mm), but usually only a few.
(b) Light AAA of intermediate calibres, typically 25-28 mm.
(c) Light AAA of the 37 - 45 mm calibres.
(d) Heavy AAA with time-fused HE shells of 88-90 mm calibres.
(e) Dual purpose guns capable of dealing with unarmoured ships and serving as heavy AAA; calibres 100 - 133 mm.
A German ship might have 20 mm, 37 mm and either 88 or 105 mm by 1939, for example.
Another example: The USN was very late in adoption of adequate light AAA and often only had 12.7 mm machineguns and 127 mm heavy AAA on its cruisers by the late 30's. Later it added 1.1" (~28 mm) weapons and then re-armed thoroughly by mid-WW2.
Wartime experiences showed that machineguns were almost 100% useless. The only utility was in deterring skip bombing and even that wasn't a safe bet.
|20 mm Oerlion|
Light AAA of around 20 mm calibre proved to be weak in effect and range, but was still worthwhile because the mounts could be made so small and lightweight that you could always find some spots otherwise left unused for such guns. Fire control was done with cheap ring sights and tracers only. The personnel demand wasn't great either - some surface gunnery sailors could double as 20 mm AA gunner and ammo porters, for example.
Intermediate calibres were promising, but the mounts ended up being about as demanding as 37-40 mm mounts while intermediate calibres lacked the range to really affect torpedo bombers or dive bombers much prior to release of their ordnance. The effective ceiling didn't prohibit promising level bombing attacks either. Finally, shells smaller than 30 mm -especially not thin-walled ones - were too weak to ensure a one-hit kill on single engine aircraft (even 37 mm was occasionally criticised for its effect). The IJN's (Japanese) 25 mm gun (developed from a French weapon) and the USN's.28 mm weapon fell into this category.
The German 30 mm Mk 103 might have saved the reputation of this calibre group if employed on 20 mm-like mounts late in the war, though.
37-40 mm were more promising calibres, and due to different designs the 40 mm solution in shape of the modified Bofors weapon proved to be a very good choice (the best among the ones pursued).
Heavy AAA (anti air artillery) of the pre-1942 period was a bitter disappointment. Much noise and small black clouds, but few kills. Heavy AAA meant much weight, much top weight (especially in cases such as the high superfiring centreline 127 mm or 133 mm twin turrets), the turrets were turning slowly, fire control was inaccurate and the fuze setting was usually incorrect. Double fuses with secondary impact function wouldn't have helped much because target silhouettes were usually rather small and direct hits very unlikely. The problems were worst with some poor 127 mm designs (not the 38cal U.S. gun) and the even heavier guns. 88 to 105 mm was relatively quick-firing, but still not very effective (the Japanese had successful high performance 100 mm gun in small quantities, though).
So what would have been the optimal AAA armament by 1939, for example?
Basically you could have stuck with 40 mm quads, 40 mm twins where is no space for quads, 40 mm single mounts where is no space for twins and 20 mm mounts where is no space for 40 mm singles. Heavy AAA was actually not worthwhile, albeit 120-133 mm dual purpose guns were justifiable thanks to their surface target role when there was no space for the more effective surface target guns of 138-155 mm calibres.
Did navies or even outsiders knew about this?
Not really. There was apparently considerable confidence in the heavy AAA and the range+effect limitations of 20-28 mm guns were not self-evident either.
The USN became even fatalistic about naval air defences after its dive bombers impressed much in fleet experiments.
Now fast forward to 1942, only a three years and some radar technology advances later.
Radars and computers had helped making heavy AAA more accurate and radar proximity fuses replaced the setting of time fuses (electrostatic fuses would have been possible as well).
Suddenly, the heaviest AAA became effective. The new fuses did not fit into the smaller heavy AAA calibres at first, though. 127-133 mm calibres were OK.
By about 1944, 90 mm guns were capable of making use of the same fuses and their capability was multiplied as well.
Meanwhile, the 40 mm Bofors became understood to be the best light AAA gun. The demand for other light AAA calibres was small.
|76 mm twin|
Only a short time later by about 1945, proximity fuses were feasible for 76 mm heavy AAA. These were so quick-firing, compact, light and responsive that 76 mm was almost capable of replacing 40 mm on about a 1-for-2 basis (it was meant to happen, but turned out to be a bit bigger than this). 76 mm was capable of dealing with aircraft both in typical light AAA and typical heavy AAA situations and was thus able to replace both!
Post-WW2, 40 mm lost much relevance and few ships still received many such guns. 76 mm became more prominent until navies began to fear nuclear bombing so much that they largely shed the within visual range air defences in favour of at first very unreliable surface-to-air missiles.
Today, 57, 76 and 100 mm are popular naval dual-purpose gun calibres, with 20-30 mm being used in dedicated close-in weapons systems of often-questioned effectiveness. 40 mm guns are sometimes the lone pro forma weapon of minesweepers and the like.
114 and 127 mm calibres are in use for DP guns as well, but rather with an emphasis on surface targets due their lower rate of fire (especially true for U.S. pattern 127 mm gun).
So basically at first by '39 navies woke up to the previously widely underestimated need for naval air defence.
By 1942 ships were upgraded with more (mostly light) AAA, but wartime experiences revealed that the choice of calibres was mostly wrong.
By the time the 40 mm calibre was well-established (1943), the previously very inefficient heavy AAA had suddenly become powerful (at least for USN and RN).
By late war (late '44, '45), 40 mm was already deemed in need of a superior successor and the longer-ranged and potentially more deadly 76 mm gun was preferred, but the important fuse was not ready and upgrading hundreds of ships with new AAA would take years anyway.
Now think about it: What were the odds of outsiders getting this stuff right at the time? Almost zero in my opinion.
I strongly dislike it, but the more lever effect some small technological progress or some rather hidden property has, the lesser the ability of outsiders to guess (or analyse) correctly.
Sadly, insufficient testing may (and often did) also prevent officials from getting it right. Bureaucratic inertia, red tape, budgeting, egomaniacs in cock fights, business interests and so on may also lead to very much inadequate equipment.
See the Royal Navy's weak short range air defences in the Falklands conflict. Only the Sea Wolf-equipped ships were satisfactory up close.
Too much uncertainty about effects of technology, which happens to dominate naval and aerial warfare much more than land warfare.