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ORIGINAL: Scott_USN

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ORIGINAL: JWE

From June ’43 to June ’44, 2nd Support Group sank 23 U-boats, 6 by gunfire, none by ramming. One of the 7 was sunk by DD gunfire, the remaining 6 were sunk by 4” gunfire from Sloops.

That was just funny for some reason. I think the Sloops won out... Nerf the Sloops!

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ORIGINAL: JWE

I don't care if he's the Archangel Gabriel. To any decent artillerist, a gun is a gun, and obliquity is something we know about more than most. Who gives a crap about crush depth. Hull thickness was 21mm (some say 28mm). Kinetics is kinetics and no amount of smoke and mirrors changes that. I know, because we studied fiziks at gun skool. We learned about penny-trashun makaniks, detonation velocities, and other kool stuff like that. It was a real eye popper to me because I was just a dumbass physicist from MIT, and these were real people, shooting real rounds, from real tubes, at real targets, in real engagements. golly gee willikers it was like a jumpin frog on a hot rock.

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ORIGINAL: JWE

I don't care if he's the Archangel Gabriel.

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ORIGINAL: JWE

I don't care if he's the Archangel Gabriel.

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ORIGINAL: Monter_Trismegistos

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ORIGINAL: JWE

I don't care if he's the Archangel Gabriel.

But you should. He might came from heavens and sink your carriers with his sword.

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ORIGINAL: Fishbed

SEMI-Armor Piercing

(that will be 5 bucks, got my paypal account right?)

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rminal ballistics is not my speciality, but I had to know quite a bit about it 30 years ago. The armour penetration of a RN 4" naval gun firing AP was on the order of 100-130 mm against 30 degree obliquity armour. When you consider a submarine hull at 25 mm or so, that sounds pretty good. However at high obliquity, you have two factors to take into account--the shell tends to ricochet, and the steel to be penetrated is increased in proportion to the tangent of the obliquity. I don't have a copy of Ogorkewicz at hand, but I seem to recall the combination of both factors results in something like a reduction of 3-4 times in penetration when the shell hits at 60 degrees obliquity. Perhaps we can do a rough analysis. A submarine pressure hull is basically a length of sewer pipe made of high-quality steel armour plate floating very low in the water. Its cross-section is oval (at the ends) and circular (in the middle). For the U-VIIB, the diameter was about 4.7 meters, and the draught when surfaced was 4.4 meters, so we're talking about the pressure hull making a 60 degree angle at the surface of the water--that's rather high. It looks like the average angle at which the shells hit the pressure hull was about 15 degrees--i.e., the armour was at about 75 degrees obliquity. I don't think the shells will usually penetrate at that angle--they'll bounce off.

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Pressure hulls and subs were NOT armour plated thats a major difference a 4" could prob penetrate like 160mm-200mm of steel even quartered that's enough.

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ORIGINAL: bklooste

Pressure hulls and subs were NOT armour plated thats a major difference a 4" could prob penetrate like 160mm-200mm of steel even quartered that's enough.

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ORIGINAL: John Mark

I always assumed that was a lot of critical equipment between the pressure hull and the outer hull such as ballast, pumps, and such. Am I wrong? If these were "compromised", surely the sub would be in trouble.

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ORIGINAL: John Lansford

Were WWII subs double hulled?  I didn't think they were.  However, if a sub is using its deck gun at a merchant then I'd expect the merchant to fire back at the conning tower area, which would represent the largest target on the sub.  A hit there is most definitely not striking at an angle like it would on a rounded hull, and a 4"-5" gun would have enough penetration/explosive power to do some damage.

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ORIGINAL: John Mark

I always assumed that was a lot of critical equipment between the pressure hull and the outer hull such as ballast, pumps, and such. Am I wrong? If these were "compromised", surely the sub would be in trouble.

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ORIGINAL: oldman45
If you went thru the hull you were in the people tank, there were no double hulls. Another thing to remember, if you are able to get a hit or near miss that caused the ballast tanks to leak the boat is going to sink. They are external to the pressure hull. In other words, you don't have to penetrate the pressure hull.

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ORIGINAL: oldman45

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ORIGINAL: John Mark

I always assumed that was a lot of critical equipment between the pressure hull and the outer hull such as ballast, pumps, and such. Am I wrong? If these were "compromised", surely the sub would be in trouble.

If you went thru the hull you were in the people tank, there were no double hulls. Another thing to remember, if you are able to get a hit or near miss that caused the ballast tanks to leak the boat is going to sink. They are external to the pressure hull. In other words, you don't have to penetrate the pressure hull.

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ORIGINAL: Zebedee

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ORIGINAL: oldman45
If you went thru the hull you were in the people tank, there were no double hulls. Another thing to remember, if you are able to get a hit or near miss that caused the ballast tanks to leak the boat is going to sink. They are external to the pressure hull. In other words, you don't have to penetrate the pressure hull.

The Shark projectile Harry mentions was designed to explode next to the hull of u-boats.

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ORIGINAL: herwin
Yes, to produce a mining effect. Most of the time late in the war, escorts used shallow-fused DCs to kill surfaced subs. Earlier in the war, DCs were fused to go off at 50 feet (or even at 150 feet!), which was too deep to do any damage to a surfaced U-boat.

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ORIGINAL: Dili

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Pressure hulls and subs were NOT armour plated thats a major difference a 4" could prob penetrate like 160mm-200mm of steel even quartered that's enough.

If it bounces it doesn't matter how much it penetrates. A very heavy round at high velocity might shatter and dent the surface, but much of energy is diverted.

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f it bounces it doesn't matter how much it penetrates. A very heavy round at high velocity might shatter and dent the surface, but much of energy is diverted.

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Point blank, a 4" destroyer AP shell would have been good for at most 100-130 mm of penetration. What the escorts and small DDs actually mounted was a low velocity (1300 fps) LA weapon intended for engaging subs. The kinds of shells were HE, shrapnel and illumination, not SAP or AP.

That said, I also have to point out that the steel in WWII pressure hulls is very hard to tell from homogenous steel armour. Most nations used the same high tensile steel for both light armour and submarine pressure hulls.

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ORIGINAL: bklooste

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Point blank, a 4" destroyer AP shell would have been good for at most 100-130 mm of penetration. What the escorts and small DDs actually mounted was a low velocity (1300 fps) LA weapon intended for engaging subs. The kinds of shells were HE, shrapnel and illumination, not SAP or AP.

That said, I also have to point out that the steel in WWII pressure hulls is very hard to tell from homogenous steel armour. Most nations used the same high tensile steel for both light armour and submarine pressure hulls.

Its still not going to compare to face hardened plate where most Naval tables are written such Class A . KC n/A or CA. Also I have serious doubts based on HE vs tank armour that a 100 mm HE round is not going to penetrate 40mm of steel.

Still subs were small targets carried a decent guns and torpedoes . Turning to face and ramming would seem a decent choice at the least for minimizing damage to the escort vessel from torpedo or gunfire .

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ORIGINAL: bklooste

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ORIGINAL: Dili

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Pressure hulls and subs were NOT armour plated thats a major difference a 4" could prob penetrate like 160mm-200mm of steel even quartered that's enough.

If it bounces it doesn't matter how much it penetrates. A very heavy round at high velocity might shatter and dent the surface, but much of energy is diverted.

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f it bounces it doesn't matter how much it penetrates. A very heavy round at high velocity might shatter and dent the surface, but much of energy is diverted.

But bouncing is MUCH more likely for armour plate . The main reason for surface hardening plate is to prevent penetrations. Steel would be much easier to penetrate than plate at the same angle .

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ORIGINAL: herwin
The kinds of shells were HE, shrapnel and illumination, not SAP or AP.

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ORIGINAL: herwin
Homogeneous steel plate armour is what submarine pressure hulls are made of. You're thinking of face hardened armour, but the minimum thickness of face-hardened is several inches--it's designed to shatter AP projectiles, but homogenous functions more to cause the shell to ricochet.

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ORIGINAL: Zebedee

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ORIGINAL: herwin
The kinds of shells were HE, shrapnel and illumination, not SAP or AP.

Herwin - I've come across after action reports where eg the Starling specifically is mentioned as having fired HE shells against u-boats. (eg U-473, although despite the claims of opening up the hull with 3 shells out of the 130+ fired the claims may be optimistic given the evident need for scuttling charges to go off before the U-boat sank). Have you come across any reason why they weren't carrying SAP rounds?

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ORIGINAL: JWE

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ORIGINAL: herwin
Homogeneous steel plate armour is what submarine pressure hulls are made of. You're thinking of face hardened armour, but the minimum thickness of face-hardened is several inches--it's designed to shatter AP projectiles, but homogenous functions more to cause the shell to ricochet.

Absolutamundo. Metallurgy of armor is way different from the metallurgy of a hull. The carbon and specific alloy content that makes for good armor, is pretty much unacceptable for a sub hull. Ductility, homogeneity, and elasticity are the prime referents for a hull. So you can’t think in terms of FH, or KC, or any of those. Gotta think in terms of rolled, mild, homogeneous. Today, sub hulls are way different, but steel hulled surface ships are still built from high tensile Ni-chrome or chrome-moly mild steels, instead of the lighter/stronger alloy steels available, for the same reason: ductility, homogeneity, and elasticity.

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ORIGINAL: JWE

Absolutamundo! Nathan is really good on armor metallurgy, especially Naval armor metallurgy. I remember some conversations we had a few years ago on vanadium as a carbon analog. Wish he could have lectured at Sill when I was there. Guy knows his stuff.

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ORIGINAL: herwin

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ORIGINAL: JWE
Absolutamundo! Nathan is really good on armor metallurgy, especially Naval armor metallurgy. I remember some conversations we had a few years ago on vanadium as a carbon analog. Wish he could have lectured at Sill when I was there. Guy knows his stuff.

I worked with him thirty years ago, doing some of his translations from German. I suggested his initial approach to calculating the penetration of multiple armoured decks when we were looking at the Hood sinking. I ended up with copies of a number of declassified TOP SECRET reports--Security got very upset until I pointed out the declassification stamps.