RAMMING SPEED!

[herwin]

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.

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.

[herwin]

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.

You could live without that stuff as long as the pressure hull was intact.

[herwin]

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.

They had a light hull (a few millimeters in thickness) outside the pressure hull.

[oldman45]

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.

[Zebedee]

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.

[herwin]

ORIGINAL: oldman45

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.

There were ballast tanks internal to the pressure hull with sufficient capacity that if they were blown, the sub would not sink. The saddle tanks outside the pressure hull gave you the ability to dive or surface quickly, but their integrity wasn't critical to the survival of the boat.

[herwin]

ORIGINAL: Zebedee

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.

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.

[Zebedee]

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.

I did have a photocopy of the pamphlet done for the Admiralty on the Shark projectile at one point. Goodness knows where it's got to though. I've also seen US intelligence reports where they claim the IJN were developing such a projectile, although I've no idea how much truth there is in that.

Just to clarify something John Lansford brought up - conning towers were hit and penetrated by shell fire. It's only the hulls which are 'contentious' The problem with hitting the conning tower is that it doesn't result in a 'kill' unless the u-boat crew abandon ship and scuttle - I can think of one occasion where a fire broke out in the conning tower and resulted in this, although I'm sure there are more. I know absolutely nothing about ballistics and maritime engineering, but there was certainly a perceived need for a 4" shell which could sink u-boats rather than bash their conning towers about.

[bklooste]

ORIGINAL: Dili

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.

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 .

[bklooste]

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 .

[JWE]

ORIGINAL: bklooste

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 .

Hi Ben,
Harry’s thinking of the 4”/40 that was used on the trawlers (Flower, Castle, Bathurst) and Brit River class frigates. The sloops and up, as well as Can and Aus Rivers, used the high velocity 4”/45 with a decent SAP round. Gunnery table rule-of-thumb for penetration for that tube was ‘half caliber at 10 degrees half range’, so about 50+ mm at around 4000m.

Depending on the country, and the time frame, sub hulls could range from 50k psi-tensile mild steel, to 60k – 70k psi-tensile chrome-moly/manganese/vanadium alloys. Different characteristics (particularly elongation) than armor.

[herwin]

ORIGINAL: bklooste

ORIGINAL: Dili

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.

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 .

I take it that you weren't listening. 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.

[Zebedee]

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?

[JWE]

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.

[herwin]

ORIGINAL: Zebedee

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?

The low velocity guns on those smaller escorts didn't have an AP or SAP shell!

[herwin]

ORIGINAL: JWE

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.

See Nathan's site.

. . SCHIFFBAUSTAHL "Ste. 52"
. . USAGE: Large ships, torpedo boats, and submarines.
COUNTRY COMPANY TIME FRAME TENSILE YIELD Y/T % EL % RA BRINELL
GERMANY ALL 1935-1945 74 51 .69 18 c.58* 150
*Estimated

[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.

[herwin]

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.

[JWE]

ORIGINAL: herwin

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.

Cool. Nathan's retired out here in Cali now and a couple us developers who live here are going to visit him on our next beer & skittles meeting. We'll be sure to bring this note along, so he knows who you are. Should be in about a month or so, but we'll do a big report on the main boards when we get back; there's a couple things we want to know, that only Nathan can provide a trustworthy response to. I'm sure you understand.