Bofors

[Crannogman]

Running low on 4" shells (and out of fish), I put my last dozen shells into a 5000-ton freighter, which proved insufficient. I closed to under 2000y at decks awash and began to pour in 40mm Bofors rounds. 1500 HE rounds and another 200 AA (using OTC) did not make an appreciable difference, except for one lucky hit taking out the freighter's bow gun.

A 4" shell weighs 33lb, while a 40mm shell is about 2lbs. Is there any reason to expect 1.5 tons of 40mm shells to be incapable of sinking a 5000-ton ship?

[TorpX]

Originally Posted by Crannogman

A 4" shell weighs 33lb, while a 40mm shell is about 2lbs. Is there any reason to expect 1.5 tons of 40mm shells to be incapable of sinking a 5000-ton ship?

The shell may weigh 33lb, but the bursting charge is less than 1½ lbs. The bursting charge for the 40mm rd. is 0.15 lbs. Most torpedo warheads were 500 lbs., or more. The bursting charge is, I think, a better index of their relative capability.

There are many examples of submarine gun attacks that failed to sink ships, or sank them with only a great deal of difficulty. Imo, ships over 1,000 tons, and certainly those over 2,000 tons, should not be that easy to sink (with shells I mean).

If you go by the USN's official records, the tonnage of Japanese merchant ships sunk by shell fire was almost trivial. Most of those sunk in this way, were smaller ships/craft.

You didn't say what mods you are using. It can make a big difference. In RFB you can sink ships of this size with the deck gun, but I think it is more difficult than with stock. Don't know about TMO.

[Crannogman]

My only mods of note are RSRD and OTC. For reference, I had sunk a couple 4500-ton Heito Marus a day earlier using a total of 40 4" shells

[TorpX]

So, I take it you are using the stock version of RSRDC?

In stock, it is usually pretty easy to sink stuff with DG. I don't know if RSRDC would change that, or not.

For reference, I had sunk a couple 4500-ton Heito Marus a day earlier using a total of 40 4" shells

That is more or less what I would expect in the game, generally.

However, you have to realize that a 40mm gun is designed to tear up aluminum aircraft, not sink ships.

In RFB, you can sink ships fairly well, but you usually have to aim near the waterline, and be patient. The damage zones of the merchants are mostly below WL. In stock, iirc, you can hit them anywhere, and blow them up.

[Sniper297]

Silent 3ditor, open \Data\Library\shells.zon.

40mm has three types of ammo, ball for the flying machines, high explosive and armor piercing for ships.
17 is the AP, 19 is the HE.

I increased the explosive power and damage radius for those two to make it possible to sink small freighters with 10 clips or so of HE if I fire at the waterline. Got a destroyer chasing me and I can't dive for some reason I use armor piercing, but unless he's already damaged that takes 20-30 hits by which time my sub is a junkyard. Unless I get really lucky.

The modern AH-64 Apache helicopter has a single barrel 30mm gun, I've seen several videos of that gun tearing up armored vehicles and light tanks. My opinion the 40 SHOULD do AT LEAST that much damage if not more, so to me the BOFORS in game seems underpowered.

[Crannogman]

Yes, but even a heavy tank is only 70t. The Bofors as-is does seem to be decently effective for knocking out defensive weapons on the enemy ship - under 2000y, your crew should be able to score hits on occasion

[Crannogman]

Originally Posted by TorpX

The shell may weigh 33lb, but the bursting charge is less than 1½ lbs. The bursting charge for the 40mm rd. is 0.15 lbs. Most torpedo warheads were 500 lbs., or more. The bursting charge is, I think, a better index of their relative capability.

There are many examples of submarine gun attacks that failed to sink ships, or sank them with only a great deal of difficulty. Imo, ships over 1,000 tons, and certainly those over 2,000 tons, should not be that easy to sink (with shells I mean).

If you go by the USN's official records, the tonnage of Japanese merchant ships sunk by shell fire was almost trivial. Most of those sunk in this way, were smaller ships/craft.

You didn't say what mods you are using. It can make a big difference. In RFB you can sink ships of this size with the deck gun, but I think it is more difficult than with stock. Don't know about TMO.

Interesting that the 4" shell weighs 16x the 40mm shell, but its bursting charge is not quite 10x heavier (630g vs 68). Also, if http://www.navweaps.com/Weapons/Gun_Data_p2.htm is to be believed, it's only ~3x more effective (25 vs 8.3).

[Sniper297]

"Yes, but even a heavy tank is only 70t."

Main difference is it would take zero hits with a 40mm shell to sink a tank, put it in the water and it would go down by itself.

"The Bofors as-is does seem to be decently effective for knocking out defensive weapons on the enemy ship - under 2000y, your crew should be able to score hits on occasion"

Ridiculous part is the crew AI is actually pretty good at shooting down enemy aircraft, in fact a lot better than I am doing it manually. However, AFAIK there's no way to get them to load the BOFORS with HE or AP and fire at a ship, you either do it yourself or it don't happen. 4"50 deck gun is a different story, there's a mod for AA shells for the deck gun but stock game doesn't have it. I never tried the mod since the crew AI for the deck gun gets about 1 hit for 20 rounds fired even at close range when firing at ships, I can do better than that with a hangover.

There is a balance involved in hacking the shells.zon file - on the one hand it's tedious trying to finish off an unescorted merchie with hundreds of rounds, on the other hand you don't want to make the deck gun and BOFORS so powerful that torpedoes become superfluous. What I did was double the explosive power, radius, and armor piercing, then reduced the number of rounds carried (in the Data\Library\SubParts\*.sim file for the weapon). The idea is when you're out of fish and gotta sink something you can do it without wasting a lot of time, but you can't do it often because of limited ammo.

[Crannogman]

Actually, I meant have the AI use the deck gun against the waterline, while you man the AA gun and go after the merchie's gun.

I just began a career with Narwhal - 4 shells sank a 1800t freighter off the Mariannas, but it took 40% of my fuel to get there at 10kts

[TorpX]

Originally Posted by Crannogman

Interesting that the 4" shell weighs 16x the 40mm shell, but its bursting charge is not quite 10x heavier (630g vs 68). Also, if http://www.navweaps.com/Weapons/Gun_Data_p2.htm is to be believed, it's only ~3x more effective (25 vs 8.3).

You are referring to this:

Two rules of thumb about Burster Power
1) The effect of the burster may be taken as being proportional to the square root of the weight of the bursting charge.
2) ...

I've read that, and I would really like to know where they get this idea.

It doesn't seem to be supported by the laws of physics. Moreover, it seems to fly in the face of documented battle reports, both of sub attacks on ships, and warship vs. warship battles.

And, if it were really true, why would navies even bother with torpedoes and bombs; just use small or medium size guns, and shower the enemy with high volume fire, to do the job. Reported instances of successful sub DG attacks tend to stand out because they were uncommon.

Someone, a while ago, was complaining that they couldn't sink a 1,000 ton ship with 20x 4 in. shells. I posted a short summery of an attack made by the Tambor:

There are many examples of submarines requiring many shells to sink even small ships, or not being able to sink them at all. For example, it was the Tambor, iirc, that happened to see a small 'ship' that was taking supplies to the stranded garrison on Wake Is. The vessel was something less than 500 t, and clearly not a good torpedo target. They surfaced and engaged with the 5 inch gun. They exhausted their ammunition, and ended up taking out the defenders with small caliber fire, before boarding the craft, capturing the First Officer, and finally setting the craft on fire. Nor was this extraordinary. Shells aren't nearly as effective as torpedoes, and this is why the torpedo malfunctions were so disabling( and frustrating). There was really little alternative to torpedo attack, unless the targets were very small. BTW, when I use the word small here, I mean something less than 500 tons. That was the criteria used by JANAC, and they made no attempt to track or verify sinking of anything less.

[Sniper297]

I think you're looking at it bass ackwards. I'm miles away from being a math whiz, but the square root is the number which multiplied by itself is the original number. Example bursting charge 16 pounds, square root of 16 is 4, so the "proportional effect" of a 16 pound charge would be 4 pounds, in other words weaker, not stronger. Dunno if that's true or not, I gave up trying to figure out algebra and women in 1968.

One factor left out - fire a 40mm HE shell into a merchant sailing in ballast and it will make a hole in the side, probably damage some internal bulkheads. Need a lot of small holes near the waterline to sink it.

Fire a 40mm HE shell into a merchant loaded with bombs torpedoes artillery shells or all the above, all it takes is one hit to set off the chain reaction that will blow pieces of the target into another ocean. Same with tankers, got one carrying crude or empty you're gonna need a dozen torpedoes to actually sink it, deck guns and BOFORS would be a complete waste of time. OTOH if the tanker is full of avgas, one 40mm HE sparks 10,000 tons of high octane, kaboom. Rather than proportional square root math you get the big bang theory with a secondary explosion.

[Crannogman]

Indeed, the square root claim is entirely un-referenced. But that was all I could find. Another section on that website is dedicated to calculations of damage from shellfire - it is hampered by referring mostly to armored targets, but suggests that the lion's share of destruction is kinetic rather than explosive.

[Longknife]

Being pragmatic you can lay waste to the superstructure reducing it to twisted iron but if there are no holes below the WL the ship will not sink.

FWIW I gave up using the deck gun & I run from aircraft like a little girl from a spider only manning the AA as I am crash diving. While the secondary armament is no doubt fun to play with, in sim as in real life the only way to reliably put a ship down is to drive a torp into her side.

[Crannogman]

Originally Posted by Longknife

Being pragmatic you can lay waste to the superstructure reducing it to twisted iron but if there are no holes below the WL the ship will not sink.

FWIW I gave up using the deck gun & I run from aircraft like a little girl from a spider only manning the AA as I am crash diving. While the secondary armament is no doubt fun to play with, in sim as in real life the only way to reliably put a ship down is to drive a torp into her side.

I generally agree. When I first got a pair of twin 20mm guns I thought to sail with impunity. It was effective against the Zeroes for a day, but then I was out of ammunition. I generally save the deck gun for ships at anchor inside atolls, or else to finish off merchants that I have already holed. I do find the deck gun to be useful against escorts - when there's one minesweeper guarding 8 large freighters, I draw out the escort and sink them (since my long-range gunnery is quite superior) then close in to torpedo the merchies.
In the thread-leading instance, I had already expended all my torpedoes and almost all my 4" shells, and hoped a couple thousand 40mm rounds could finish the job. Unfortunately, even if they do cause damage to ships, I don't think they can really get below the waterline

[TorpX]

Originally Posted by Sniper297

I think you're looking at it bass ackwards. I'm miles away from being a math whiz, but the square root is the number which multiplied by itself is the original number. Example bursting charge 16 pounds, square root of 16 is 4, so the "proportional effect" of a 16 pound charge would be 4 pounds, in other words weaker, not stronger. Dunno if that's true or not, I gave up trying to figure out algebra and women in 1968.

I think he got the math right; it's just the 'rule' itself is questionable.

If you have a model, with a 'medium' shell with 1 lb. of TNT, you could give it a base damage of 1. A large shell with 4 lbs. of TNT, would give damage of 2, and so on. A bomb with 100 lbs. of TNT, would give damage of 10. This sounds alright, until you ask if 10x medium shell hits are really as effective as one large bomb hit. Imo, this idea fails when examined closely.

This sort of concept may make sense, if you are applying it to a damage model, where ships are defined in very simple terms, having a total number of hit points, without any specific damage zones, critical hit areas, etc. The idea being, additional damage to areas already hit/destroyed becomes superfluous, so there is a diminishing return on larger types of ordnance, and scattered hits are assumed to damage more sections.

However, in a more developed model (as in SH4), you already have limits as to how much damage a zone will take, and a floodable zone can only flood to a certain level, and no more. So, too much fire directed to a small part of a ship is likely to be wasted.