"Benefits of 8" guns vs 6" guns?" Topic

I noticed a lot of cruisers in WWII (of similar size) had either 8" or 6" guns and was wondering the advantage conferred by larger calibre guns.

Range?
A quick google showed 25k range for 6" and 30k for 8".
Since I find it unlikely either ship would be scoring hits at such long range, then range can't be a major factor.

8" guns (according to the internetz) have twice as big a shell. But I presume the 6" would have had a higher rate of fire, and more guns were carried. So at practical ranges against cruiser sized and smaller targets, wouldn't a deluge of lighter shells be superior? I.e. how useful would an 8" gun be against bigger ships anyway?

In WWI there seemed clear distinctions between the old armoured cruiser and light cruiser/destroyer leader types, and different armament made sense, given the very different roles.

But in WWII I'm wondering – why the 8"?

I can see the 'difference' in a escort/AA-cruiser like the Dido with high-elevation 5.25 guns etc, but how does a 8" and 6" gun cruiser vary in their role etc?

Try economics, during the interwar years many navies explored costing cutting exercises. A 6" gun is cheaper and quicker to build as well as transport.

Larger shells have greater penetration and do more damage. And you seem to dismiss the abilty of guns hitting at these longer ranges, when they actually can hit pretty far out. So range should be factored back in.

The 6 in guns did have a higher rate of fire, but navies preferred the 8 in guns. 6 in guns ewre common in light cruisers, 8 in in heavy cruisers. The Japanese navy had one class (Mogami IIRC) that started with 6 in guns and was up-graded to 8 in guns, and major modifications to bring the ship up to heavy cruiser status.

There was a pre war arms control treaty (Washington Treaty?) that limited the number of heavy cruisers that the signatories could field but it didn't apply to cruisers whose largest armament was the 6" gun.

Robert

Treaty considerations were a reason. At the end of WW1 the Armoured Cruiser was replaced by the Heavy Cruiser. Because the British had a class of new cruisers with 7.5" guns they argued for an upper limit of 8" and for the traditional scout cruiser side to be 6". The RN had already established from combat experience that the 4" was inadequate as a ship killer.

Your question wonders why, but during the inter war years many naval authorities wonder why too? There was considerable argument for both sides regard 8" and 6". Proponents of the 6" gun argued that because of the rapid rate of fire they could overwhelm an 8"gun cruiser with hits.

The 8" gun proponents argued that the larger shell gave a greater accuracy at long ranges as well as a heavier hitting power. Therefore the 6" gun cruiser would not be able to get close enough to use its higher rate of fire.

WW2 did not really see either side winning the argument. Many actions took place at quite short range. In such actions the penetration of the 6"was usually quite adequate and the high rate of fire spectacular. Yet when the 8" did hit and burst it was capable of producing spectacular results. The battles around Guadalcanal showed that both types were valuable.

I have recently been re-reading many of the above actions and I'm not sure the battles were won by one size or the other.

Certainly for shore bombardment the 8" was better for long range work and against fortifications. But then again the 6" cruisers proved with the bombardment of Munda (For example) that the number of shells they could lob onto a target was pretty destructive too.

The advent of more aircraft meant that the original role of the light cruiser in the scouting role, was no longer applicable. But this was not fully realised until the war was under way. The role of the Heavy Cruiser as destroyer of enemy scouts was also no longer required.

As a result of this cruiser designs became larger and the role of the two types merged.

British understanding was that most of the waters they expected to fight in had low visibility most of the time, thus the light cruiser with its rapid fire guns would be sure to get in close, and generally it could carry more of these weapons.

For other areas, such as the Pacific, South Atlantic and Mediterranean it was expected that the heavy cruiser would prevail.

Thus the argument was never really resolved and both types were built.

The US produced the Brooklyn class with fifteen 6"guns, but never attempted to go more, because it was found that there were structural weakness problems with that many guns and the resulting long hull. The USN went to twelve guns for the Cleveland class as well as a high number of heavy AA. (5")

The British went to twelve 6" after considering fifteen. But war experience showed that nine guns were quite adequate and were not too concerned about removing a turret to add more AA guns.

Gun technology resulted in an extremely high rate of fire six inch gun being produced for the USN in the Worcester class. But at the same time it was realised that the same advances could be applied to the 8" gun, hence the HUGE Newport News class ships.

Perhaps the last word in the argument has come via modern times. It was presumed that extremely high rate of fire guns would be adequate for shore bombardment. However it has been found that the actual hitting power is lacking, hence recent debate about making new era destroyer guns of 8" type.

Oh…and those escort cruisers. These really only came about just before WW2 when the British decided to rearm some of the old C class as AA ships to meet a growing threat. This sort of vessel was seen as of great value for protecting the fleet and newer vessels requested. This resulted in the Dido class and the US Atlanta class ships, a type not seen in other navies.

But the role of the AA cruiser was very role specific as their guns proved inadequate for other fleet work due to a lack of hitting power. The Japanese, who had good reason to need them, only converted one light cruiser to the AA role (ISUZU 1944) but built the very large destroyers of the Akatsuki class for that role. The role of these ships ended with the end of WW2 as by then improved AA guns for other ships rendered them unnecessary.
Some soldiered on for a few years as they were new ships, but their role had really been taken over by the CAP of the carriers.

The 8" has a slight utility against larger (battleship) targets, the 6" is sort of "yeah, good luck with that".

Besides, the naval limitations treaties set 8" as maximum shell size, so if you wanted the heaviest guns, that's what you used.
-Kle.

@Hardrock

I'm trying to find out why the 8" guns were better. Navies did seem to build 'em (although the 6" stuck around longer after WWII?) but I'm wondering about the pros v cons.

Of course bigger shells do more damage (they weigh twice as much, as I pointed out). But relative 'weight of fire' might be the same? I.e. the 6" might fire twice as fast/there are 12 6" guns on a cruiser but only 6-8 8" guns.

I did dismiss the range, as I am simply dubious anyone would be hitting at 20+ km (the earth is curving at that distance). I think the record naval gun hit was around this range (the battleship HMS Warspite vs some Italian cruiser and that was considered a 'freak' shot) so I feel it is kinda academic. I mean you could shoot 100km but in WWII they didn't have precise guidance like we do now.

WWI 'armoured' cruisers and 'light' cruisers were definitely different in role and use. Were WWII 8" cruisers used differently than the so-called 'light' 6" gun cruisers?

@Toaster. I suspect you may be right about the Washington Treaty but what made the 8" gun more desirable in the first place, is what I am curious about.

Were 6" guns better against light targets (destroyers etc) and 8" better to fight other cruisers? How is a 'light' and 'heavy' cruiser defined in WWII? Both seemed to weigh around 10,000-12,000 tons.

EDIT: Mal I posted at the same time you did – thanks for your in-depth comments.

Glad to be of help evilleMonk.

How is a 'light' and 'heavy' cruiser defined in WWII? Both seemed to weigh around 10,000-12,000 tons.

It was a naval treaty definition.
Heavy cruisers had guns of 7.5"and larger.
Light cruisers guns of 6".

I've yet to see a conclusive argument on which group the Soviet Kirov class fall into with their 7.1" guns!

As mentioned – light/heavy cruisers were defined by gun size. Had nothing to do with hull size or armor.

As far as the "which is better" debate for 6" or 8" guns, it was never resolved before naval gunnery took a back seat to anti-ship missiles. Personally, I think there's a reason for both.

Naval Thunder confers a rate of fire bonus for 6" over 8" guns at close range, so in the game each type has its own advantages as well.

navalthunder.com

Mal

Kinda summarising a few points:

So unlike WWI cruisers there was no specific role difference (except specialist AA vessels) – 'classes' were simply defined by the gun size. A Washington Treaty definition.

And 8" and 6" cruisers served similar roles, although the 6" was supposed to work better in more confined areas. 8" was envisioned more for long-distance patrols.

6" rapid fire proved useful in confined night actions, but the 8" hitting power and long range was good too (especially for shore bombardment). So there was no particular 'best' solution

…and then, even as now, people aren't sure 'which was best'

I'm curious – I presume 8" guns could punch through heavier armour. I.e. could they sink a pocket battleship or Scharnhorst class battlecruiser when a 6" couldn't…

PS: I saw the article on 8" guns on destroyers – which is what got me curious about this in the first place!

Of course, the River Plate action demonstrated the value
of the 6" in support of the 8" cruiser.

Although HMS Exeter was badly knocked about, her consorts
were able to inflict, with their 6" guns, enough damage
to drive the enemy to bay, and to cause her captain to
make the decision to scuttle her.

Bigger is better!

The distinction between light and heavy cruisers is pretty vague by the middle of WW2. The later Town class British cruisers Belfast and Edinburgh were 6" "lights" but were as big and as tough as the 8" County class. The US Brooklyns and Clevelands were for all intents and purposes heavy cruiser sized and armored with 6" guns while the earlier US Treaty cruisers of the Northampton and Pensacola classes were 8" vessels with lighter armor than the 6" Brooklyns and Clevelands. Both the US and UK at the same time built and deployed the very light AA cruisers of the Dido and Atlanta classes armed with 5.25 or 5" DP weapons and virtually no armor that were by WW2 standards, just a hair above being very large destroyers.

As Mal points out, the US DesMoines class at the end of the war ran to 18,000+/- tons with semi-automatic 8" guns was actually larger than many WW1 era battleships.

And 8" and 6" cruisers served similar roles, although the 6" was supposed to work better in more confined areas. 8" was envisioned more for long-distance patrols.

That was pretty much the pre-WW2 way of seeing it. But war experience is cloudy. The slug out battles off Guadalcanal took place at such close range that 6"guns could penetrate any Japanese cruiser present. The 8"guns merely gave a harder whack after penetrating the same armour.

The Kongo class battleship/battlecruisers did not take too kindly to being thumped with 8"rounds at close ranges and the 6" chewed their upper works to bits. But in that instance it did need an 8"to do anything significant to flotation, steering etc.

Having just re-read much of that while recovering, I remain as undecided as ever as to which was best. The fire power of the US 6"gun cruisers was impressive, yet the hitting power of the 8" worked well.

As to roles. The light cruiser was seen as a scouting unit prior to the war, but this role was quickly taken from them by aircraft because of the range of planes. Also it was quickly found that a lone ship was a sitting duck if at the mercy of massed air attacks, so it was not such a good idea to send a light cruiser out to scout.

It was pretty much the same as most wars. What the planners planned and built for, was overcome by the realities of what was needed once the shells and bombs started to fly.

The Alaska class heavy cruisers are an example of that. They were built as large heavy cruisers, not battle cruisers. Although the role as envisaged was much the same. This was because the Japanese were thought to be building similar ships to go raiding with. But although the Japanese almost did build some, the idea was eventually dumped by the Naval High Command because their combat policy was to seek the ultimate show down surface battle. Therefore raiding (such as anti submarine protection) was given a very low rating on their priority list. In such a battle those ships would have been useless, but war experience showed that if they had been built they would have been excellent carrier escorts which would have freed up the Kongo class for other duties. The Alaska class ended up as fast carrier escorts too.

Another role envisaged for the Alaska class had been as killers of German Pocket Battleships. But the enormous advances in aircraft really put the raider out of business by 1942. The ocean was no longer a place they could hide once aircraft with long range were in service.

Pre-War planning does not always work in the real thing.

As stated above, the Washington Naval Treaty defined a cruiser as something with 8" guns. None of the major navies wanted to risk being outgunned, so everyone went to the upper limit in gun size immediately -- nearly all of the cruisers built in the late 1920's and early 30's were 8"-gun heavy cruisers. When the London Naval Treaties made two classes of cruiser and put tonnage limits on each, the 6"-gun cruiser became worth considering again, which is why most of the late-30's cruisers used the 6" gun.

Perhaps the last word in the argument has come via modern times. It was presumed that extremely high rate of fire guns would be adequate for shore bombardment. However it has been found that the actual hitting power is lacking, hence recent debate about making new era destroyer guns of 8" type.

The US has already started fielding 155mm guns on the latest flight of Arleigh Burkes, and they are back-installable to the rest of the Burkes and Ticos.

I don't think you need to go to an 8". The 155mm does simplify supply. Got a container full of Army artillery shells? Yeah, we can use those in the (naval) guns.

Overall throw weight over time of the Newport News class is disgusting (nearly on par with an Iowa!), but they run through their ammo bunker in a hurry.

Comparable throw weight to an Iowa is good for shore bombardment. . . but it's not really fair to the Iowas to compare them. The Iowas were designed to defeat other battleships.

Besides – I'd wager the "Iowa throw weight" figures you're including aren't including the massed 5" shell fire that could be brought to bear as well.

But at the same time it was realised that the same advances could be applied to the 8" gun, hence the HUGE Newport News class ships.

Salem is preserved as a museum in Quincy, Ma.
-Kle.

@TheDreadnought: Post-modernization, the number of 5"/38s is equal between the two hulls! The Iowas only gave up 4 5"/38 turrets total, two per side, so there's not a *huge* advantage there, anyway.

Let me run the numbers:

Des Moines/Salem/Newport News throw weight:
Main Battery: 335lb shells x 9 tubes x~10rds/min = 30,150lb/min
Secondary: 60ishlb shells x 6 tubes x ~15rds/min= 5400lb/min
Total: 35,550lb/min

Iowa-class throw weight (pre-modernization):
Main Battery: 1900lb HE shells x 9 tubes x~2rds/min= 34,200lb/min
Secondary: 60ishlb shells x 10 tubes x~15rds/min= 9000lb/min
Total: 43,200lb/min

post-modernization:
Main Battery: 1900lb HE shells x 9 tubes x~2rds/min= 34,200lb/min
Secondary: 60ishlb shells x 6 tubes x ~15rds/min= 5400lb/min
Total: 39,600

In all cases, I'm only giving half the secondary battery, since the other half would be masked by the hull of the ship. Also, note that the Iowas are firing at Max rate, while the Salems are at Sustained rate. I couldn't quickly find the sustained rate for the 16" Mk 7 guns.

Seems I was right on ("nearly on par"); unless the Iowas can only sustain 3 rounds every two minutes, giving a main-battery throw of 25,650 lb/min, total throw of 34,650lb/min. Advantage to the Salem-class in that case.

Some other factors to consider:

If I remember right:

In WWII and WWI, most 6" shells were cased, and the shells were relatively man-handleable. This greatly increased the rate of fire per barrel, and also greatly reduced the chance of magazine explosion. I believe the Brooklyns for example could fire off their entire magazine in about 10 minutes, and the rate of fire was one round every 12 seconds for each barrel.

8" shells, until the Des Moines, were bag-charged. The shell required machinery to load, and the charge was silk-wrapped just like battleship charge. This resulted in a slower rate of fire and more vulnerable magazines.

You don't necessarily have to punch through armor to put a ship out of action, and the 6" of the later cruisers were pretty good at smothering a target.

I seem to recall that, in an emergency (such as a battle), at least one of the Brooklyns was recorded as firing something along the line of six rounds per gun per minute in a night action in the Solomons, which meant it fired 90 six-inch shells per minute for several minutes.

Even given the state of USN night gunnery in 1942, I would not liked to have been on the IJN ship on the receiving end of that barrage.

Another part of the equation is the armor of the target. Most British and Japanese crusiers had 1" gun houses and spinter armor conning towers. So 8" or 6" would dispatch a turret fairly easy. US and Germany had armor on their turrets so the heavier shells were needed to knock them out. Some US cruiser turrets even took 8" shells without being destroyed.

To temporarily hijack my own thread – Mal, I saw you mentioned as being involved in GQ III in another thread.

Do you know Australian distributers for GQIII? To get it direct seems a fortune… (I have GQ I and II from when I was a kid and I am considering upgrading…)

Back on topic:

Thanks for all the useful replies!

So 8" guns have recorded instances of penetrating BC class ships whilst 6" are of course useful for scrubbing away upperworks… (and in British and Japanese cases, turrets as well)

Lion in the Stars -

Well looks like the pre-modernization Iowa has about a 21% throw weight advantage over the Newport News. . . and again I go back to, the Iowa was designed for maximum penetration, not maximum saturation.

As far as the post-modernization goes, you're not making a valid comparison, unless you want to calculate "throw weight" for nuclear-armed tomahawk missiles. I'd imagine, the throw weight on a Phalanx is no slouch either (a couple of them per side), since we're ignoring magazine capacity.

No, the 2700lb 16" Mk8 APC shell was designed for max penetration. The 1900lb HE shell was the same shell as used since the USN went to 16" guns. That's all the way back to the Colorado-class, from just after WW1. You still need 'saturation' to be able to hit a battleship at distance.

Still an advantage to the battlewagons, but for a mere cruiser to be in the same lbs/min league as a battleship is scary. There's a reason why we disallowed the Des Moines class CAs and Worchester-class when we were playing Seapower!
=====

Ooh, I just found a different sustained rate of fire for the 8" automatics. The wiki entry for the 8"/55 mk16 gun itself says 10 rds/min, while a comment from the Des Moines-class cruiser entry says "capable of sustaining 7 shots per minute per barrel, or about twice that of the Mk12." If the earlier guns only have a 3-4 rds/min rate of fire, that's a significant impact compared to the 10 rds/min for a 6".

Let's see here:
6" guns: 150lb shells x 12 tubes x 10 rds/min = 18,000 lb/min

8" guns: 335lb shells x 9 tubes x 4 rds/min = 12,060 lb/min
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Throw weight for a nuclear weapon? I'd have to include the nuclear 16" shells, and who the devil uses nukes for shore bombardment?

Besides, the Des Moines had been retired by then, so I guess I was dissembling a bit…

evilleMonkeigh…and anyone else in need of a copy. Contact me on mgwright@bigpond.net.au and I can help with GQIII. I also have copies of Deadly Waters, my WW2 convoy game.

The issue of the benefits offered by 8" guns over 6" guns is someone nebulous.

A cruiser armed with 6" guns can fire far more rapidly that a similar ship armed with 8" guns.

Conversely, the 8" shell, weighing "about" 2.5 times as much as the 6" shell, delivers far greater hitting power and the 8" gun can shoot farther than the 6" gun.

However … and it is a big however …

IF a ship is firing corrected salvos, meaning that each successive salvo is fired only after seeing splashes from the prior salvo, at any range over 10,000 yards BOTH guns are restricted to the SAME rate of fire.

Of course, a ship armed with 6" guns can, and often did, op to fire at a more rapid rate. However, the additional salvos are not corrected fire, and thus, by their nature, are much more likely to be inaccurate.

At the battle ranges that the USN expected to fight at (i.e., greater than 20,000 yards), even the 8" guns rate of fire would be significantly reduced if corrected fire was being used – and at such ranges, it was far more necessary to do so.

Where the capability of 6" armed ships definitely stood out was in night combat where, by its nature, the fire was seldom corrected and, when it was, the time of flight of the shells was so short that the guns could actually be fired at their maximum rate.

BTW, this same problem existed with the theoretical firing rates of destroyer guns, usually 5". While the gun could be fired at copious rates, the time of flight at anything over 10,000 yards was such that the 5" could fire no faster than the bigger gun types IF corrected fire was used.

So, the less than direct answer to part of your question is that smaller gun types offered a higher rate of fire that could often be realized only at close ranges, while the larger gun offered more range and higher hitting power as long ranges. Certainly the USN preferred the later because their doctrine called for fighting long range day-time battles, while the RN, in part, preferred the later because they expected to fight at closer ranges where the higher ROF would be utilized.

It is, however, also true they no navy found its prewar battle doctrine to be inclusive of the fighting they found themselves engaged in … :)

Mark

In the book "Battleline: The United States Navy 1919-1939" by Thomas Hone & Trent Hone, they show typical cruising formation. In the cruising formation, the DD's form the outer circle (No. 3) behind the submarine area and distant screen. The inner circle (No.1) was comprised of the BB's, Fleet Train, & CV's. The BB's were at the front of this circle with the Fleet Train in the middle and CV's trailing. Circle No. 2 was comprised of CL's and CA's. The front half of this circle was made up of CLs and the back half was made up of CA's. I assume the CL's were in front of the BB's to fend off enemy DD's torpedo attacks with their higher rate of fire. Then maybe the CA's with their longer range guns wouldn't have to make up so much range to enter the engagement. Of course when the BB's were lost at PH all this doctrine kind of went out the window.

I recall reading the following about the "after the design" and "after the learning" use of the 6" and 8" cruisers in the early period of the Pacific Theater in WWII.

Early, the US tactics involved getting into effective (shorter) firing range for actions which involved a number of cruisers and destroyers on both sides. The US/Austrian/Dutch forces lost heavily because the Japanese had excellent optical sighting and unexpected, big, fast, heavy warhead long lance torpedos, which were fired and hit even before the start of gunfire at these ranges.

The US had excellent radar, which could find and trace Japanese ships well before they themselves could be seen, but the US did not make a lot of use out of this information and often were confused by indifferent tactical planning and ground clutter returns from the many islands.

Later, the US regained the upper hand by firing under radar control at maximum ranges and smothering the Japanese ships with fairly accurate fire, while the Japanese torpedos were out of effective range and while the Japanese were surprised and under handicaps of only having dim knowledge of the location of the US ships.

Under this situation, the Brooklyn class 6" cruiser was a gem to use. 15 barrels firing at a high rate could assure some hits just by statistics, whereas fewer 8" shells would be unlikely to hit. Since the shells were dropping at long range, hits would be on the top armor rather than the side, so penatration was not an issue. (Although such ships were practically unarmored).

There is some resembalance with the pre-dreadnought debates between a smothering fire of smaller guns on the topworks or the need for a few deadly hits.

"The US had excellent radar, which could find and trace Japanese ships well before they themselves could be seen, but the US did not make a lot of use out of this information and often were confused by indifferent tactical planning and ground clutter returns from the many islands."

By 1944-5 that is true. But radar wasn't nearly as trustworthy or dependable earlier in the war…so the answer to the question changed over time. If you have the advantage of fire control radar and rapid firing guns -- as the US had at Empress Augusta Bay -- then 6" armed ships would probably win over ships with 8" guns and optical sights. But you have to realize that one lucky hit from an 8" gun can change the equation very quickly so it's never a sure fire lock.

BTW, American skippers didn't appreciate the range of Long Lances at any point in WW2. Later in the war they appreciated that some Japanese torpedoes had superior range , but didn't really appreciate the degree of difference.

Wasn't the fire control on the Bismarck taken out by an 8" shell?