Intermediate Naval Guns - 1914 to 1945

Driftless

Donor
I posing a thread that covers Naval Guns:
* Intermediate size (I'm arbitrarily picking 20mm to 175mm)
* International - US, Britain, Japan, Germany, France, Italy, etc. (CryHavoc101 had a great British thread a while back)
* From the start of WW1 to the end of WW2

* Most importantly - why were those particular sizes chosen. What were their virtues, what were their limitations?

For example: Why did the US more or less standardize on 3" & 5" guns for DE's & DD's (as well as being secondary armament on bigger ships)? Why not 4" or 6" guns? What were the technical virutes of the Bofors 40mm gun that led to near universal acceptance in WW2?

Fire away!
 
I posing a thread that covers Naval Guns:
* Intermediate size (I'm arbitrarily picking 20mm to 175mm)
* International - US, Britain, Japan, Germany, France, Italy, etc. (CryHavoc101 had a great British thread a while back)
* From the start of WW1 to the end of WW2

* Most importantly - why were those particular sizes chosen. What were their virtues, what were their limitations?

For example: Why did the US more or less standardize on 3" & 5" guns for DE's & DD's (as well as being secondary armament on bigger ships)? Why not 4" or 6" guns? What were the technical virutes of the Bofors 40mm gun that led to near universal acceptance in WW2?

Fire away!

That Cryhavoc fella is over rated IMO :eek:

I'll have a pop at the Bofors 40/60 vs Pom Pom 2 Pounder

The advantage the Bofors had over the British Pom Pom was one of Weight, Simplicity and effectiveness of the ammunition.

For example a Quad Bofors setup was 10 Tons while the 8 Barrelled 2 Pounder Pom Pom gun was about 16

The British weapon was significantly more complicated and its ammunition had a Lower MV than the Bofors gun

Given the Bofors Longer Barrel this gave it a range advantage over the Bofors gun and indeed when presented with both British made weapons for testing the US Navy choose the Bofors gun.

I suspect that it was also easier to build than the somewhat 'clockworks' 2 Pounder system.

The Bofors proved its worth during the war and in the US Navy it replaced the 1.1 Inch AA Gun and eventually would start to replace 20mm Weapons (found to be largely ineffective) as well as 5"/38 Mounts in some ships (ie the later Atlanta Class ships where it replaced the 'side' guns due to stability issues) - it was also due to its light weight able to be mounted higher up with less stability issues than comparable heavier systems as well as pretty much anywhere it would fit.

However the Pom Pom remained the principle close in AAA weapon of the Royal Navy and while it might not have had the effective range of the Bofors it was, due to its combined Higher ROF per mount (A formidable 800-900 RPM on the Octuple guns) very effective against dive bombers and later in the war against Kamikaze aircraft.

One of the stories often used to denigrate the weapon is the issues experienced on Repulse when her weapons kept failing during the attack that would sink her. This as I understand it was due to ammunition stocks taken from Singapore - turned out that they had not been stored correctly and the tropical conditions had taken their toll and this drove many of the issues experienced that day.

Also while the weapons had a very high ROF pre-1942 the ammo lacked tracer and therefore aircraft attacking a ship would not experience the somewhat off putting effect that hundreds of glowing 40 mm shells streaming towards it might have otherwise had and might not realise that it is under fire unless of course it gets hit.

This issue was resolved from 1942.
 
For example: Why did the US more or less standardize on 3" & 5" guns for DE's & DD's (as well as being secondary armament on bigger ships)?

I think the US designers just like neat numbers (others liked neat weights of shells)?

They used 3", 4" and 5" as well as 6",7",8",10",12",14",16" note no 1/2 or .1 sizes (apart from one set of 4.7" guns bought from GB)

http://www.navweaps.com/Weapons/WNUS_Main.htm

As to why they used 3" and 5" most in WW2 well 5" is (especially the 5"/38) about the best weight (ie the most weight a single man can handle fast easily) this makes it a good choice for a fast firing gun for AA or lighter surface targets.

Gun - shell/loading weight
3"/50 - 13.1/24 Fixed
4"/50(old)- 33.0/62.4 Fixed
5"/38 - 55.18/
[FONT=Arial,Helvetica]55.18 Separate

I think the USN would have been happy with just using the 5"/38 DP gun for everything (less than 6" surface fire) but they needed something for smaller ships and of the choices (3" or 4") and the 3" offered a bigger gap from the 5" and was still in service so was picked as the standard.

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Whats the trade-offs

I posing a thread that covers Naval Guns:
* Intermediate size (I'm arbitrarily picking 20mm to 175mm)
* International - US, Britain, Japan, Germany, France, Italy, etc. (CryHavoc101 had a great British thread a while back)
* From the start of WW1 to the end of WW2

* Most importantly - why were those particular sizes chosen. What were their virtues, what were their limitations?

For example: Why did the US more or less standardize on 3" & 5" guns for DE's & DD's (as well as being secondary armament on bigger ships)? Why not 4" or 6" guns?

Fire away!

Path dependency can be a big deal. The US started to go down the 5 inch gun route for its destroyers and primary secondary armament pre-WW1 as the 5/51 was adapted for anti-torpedo boat work on the dreadnoughts. After the war, there is a huge honking stockpile of 5/51 ammunition, as well as 5/25 AA ammunition, so why not design ships to use it instead of spending money to develop a weapon that is just slightly better but Congress won't fund.

More realistically, the question is what set of trade-offs are considered acceptable for a given mission. Let's look at the main armament of a destroyer for the various problems it might be used to solve:

1) Medium anti-ship (sufficient to ruin a destroyer's day, sufficient to sink a merchie) If you want more anti-ship capacity, you'll probably want a longer gun, firing a heavier shell, and probably a wider shell as well. That means fewer rounds stored per meter cubed in the magazine, a bigger firing mount footprint, more crew etc. It still won't be enough gun to really scare away light cruisers and above (an Atlanta or DIDO will avalanche a DD with ROF, a Cleveland will pound away at longer range with heavier shells etc).

So the goal of a medium anti-ship gun is something that has high rate of fire to partially compensate for the lighter shells, a heavy enough shell that can do a fair bit of damage on a few hits, a light enough shell to carry lots of them and for men to be able to reasonably hand-move quickly, accurate, and decent but not amazing range. Those constraints really limit the size. A 40mm or 57mm Bofors is light, accurate, low footprint but it can't hit a target at reasonable range. A 6 inch cruiser gun has a low rate of fire, with non-manually reloadable ammo, and is too big of a gun for a 1750 ton ship. So somewhere in the middle makes sense.

2) Low angle AA --- long range, large bursting charge, variety of fuses, rapid fire, able to quickly skew, able to quickly integrate fire control changes into solution, quick re-fusing etc. Here a long range, high rate of fire gun makes sense, it can be fairly heavily, but ROF probably matters more to breaking up a torpedo bomber attack than the size of the bursting charge.

3) High angle AA --- high rate of fire, high angle, able to easily load at high angles, very fast turning/spinning mount, easy to re-fuse shells. A high angle mount will be significantly more complex and heavier than a low angle anti-ship mount.

These are the three basic jobs a destroyer's main gun battery was expected to perform in the late 30s. The question then is what things will the navy that is buying a DD mandate as have to haves, what things are nice to have, and what things are easily trade-able. And from that set of trade-off decisions, what guns are available whose characteristics fall within the acceptable range. And will Congress/the Treasury fund buying enough of those guns.
 

Driftless

Donor
All great information so far.

I can appreciate there's a balancing act involved for all of the decisions: practical size & weight of weapon and mount compared to the ship the weapon is to be used on; along with available ammunition and other stocks.

Another set of questions:
* Why did most western navies decide on 37mm as an early standard? At least compared to 30mm or 50mm (or their relative inch - 1.5" to 2" comparison)

* I'm guessing that anything in the 6"/155mm (+/-) range regardless of origin (Germany, France, Japan, US, etc) was viewed primarily as a ship vs ship weapon
 
I would also add that the sizes we are concidering (20mm to 175mm) in the time perode we are talking about (14-45) are split into (some overlapping and will be a bit different in 14 than 45),

How is it loaded ?
- Automatic (belt, clip, etc) (7mm to 40mm with some 55/57/76 in development later)
- Hand (by how many men and how fast) and with separate of fixed charge ? (and how much help ramming etc) (and how much is the deck moving under you ?) (3" (some lighter earlier 37mm+) to 6" (with a few trying badly at 7.5"+)
- Mechanical loading with power assistance.(8"+ battleship guns)

I think you have to also conceder that for most of this period the size of guns was controlled by international treaty's (WNT/LNT/2LNT) and this continued to have effects on the sizes of guns later on in service in WW2.

The treaty's (LNT especially) basically split guns into groups by calibre size (it named the following),

- Battleships guns (16" or less but over 8")
- 8" CA guns
- 6.1" CL guns
- 5.1" DD guns
- 3"(76mm) limited in number on none warships
 
* Why did most western navies decide on 37mm as an early standard? At least compared to 30mm or 50mm (or their relative inch - 1.5" to 2" comparison)

* I'm guessing that anything in the 6"/155mm (+/-) range regardless of origin (Germany, France, Japan, US, etc) was viewed primarily as a ship vs ship weapon

I think 37mm is historic from the QF 1pdr, an enlarged version of the Maxim machine gun. Its longer range necessitated exploding projectiles to judge range, which in turn dictated a shell weight of at least 400 grams (0.88 lb), as that was the lightest exploding shell allowed under the St. Petersburg Declaration of 1868 and reaffirmed in the Hague Convention of 1899

6"/155mm was really surface only (some tried high angle AA fast firing but they didn't get any work till 50s with very complicated mounts and loading)

I think largest DP gun in WW2 (on ships in large use) was the RN 5.25" but that's a surface biased compromise that wasn't very good at AA due to being too heavy to load very fast for long (in cramped turrets).
https://en.wikipedia.org/wiki/QF_1-pounder_pom-pom#cite_note-7https://en.wikipedia.org/wiki/QF_1-pounder_pom-pom#cite_note-7
 
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