Torpedoes, running depth , barges (sealion) & small craft

[pugsville]

I read on somewhere that the sealion barges were problematical targets for British torpedoes as the running depth they were pass under the barges and not being metal the triggers would not go off.

I don't know much about torpedoes and a lot of the stuff I've read has been focused on US and German torpedo problems. Did the British have similar problems?

What depth deep torpedoes run at? Where they adjustable? Where british torpedo pistols contact or magnetic?

Would standard British torpedoes work against the sealion river barges? could they be adjusted to?

(I don't want a digression on to general sealion topics, digression onto torpedo triggers and the British side of would be more interesting)

[phylo_roadking]

H'okay....I think we're talking about the 21" Mk8 and its variants, and the Mk10. I don't have a wartime entry into service date for the Mk11...?

And for the Fleet Air Arm - the 18" MkXII and MkXIV...

I believe the running depth could be set within limits - given comments such as this for the air-dropped MkXII -

Notes: Was specified to be able to be dropped from 30 - 100 feet (9 - 30 m) at 150 knots and not dive below 60 feet (18 m) and then recover to set depth within 400 yards (360 m).

...which makes me think that at least the 18"'s running depth could indeed be "set"...but I don't know within what paramters. Usually of more interest in various discussions has been that depth that air-dropped torpedoes have to dive to first then recover Discussions on Taranto, pearl harbour...and the Panama Canal

Torpedoes do include a "depth mechanism" in their design - to keep the torpedo at its set depth as propellants are used up - otherwise it would become lighter and rise towards or to the surface! The British had a lot of issues pre-WWI during development of their torpedoes in making theirs work - "depth taking" being how it controls how the torpedo enteres the water (however delivered) and comes back up to its set depth...and how it stays there, which is "depth keeping". For several years they could make them "take" but not "keep".....or "keep" but not "take" Never both at the same time. This was IIRC cracked around 1911...

Now I just need to find out details.

[phylo_roadking]

Here's what a grotty, recovered 21" torpedo depth mechanism looks like -

The Depth Mechanism straddles the diameter of the balance chamber from top to bottom.

At the top is depth setting adjuster. This is shown cleaned to the right.

The mechanism at the bottom is a combination of hydrostatic valve and pendulum. The pendulum, dependant on gravity acts as a damper on the hydrostatic valve to stop the Torpedo 'Porpoising'.

And here's the said depth setting adjuster, cracked open -

This torpedo had been set to 34 feet

...as we can see on the setting wheel! Now we just need to find out the range of numbers around that dial

As to how the hydrostatic valve and pendulum system worked in practrice - the American equivalent, although a different mechanism used the same essential components to do the same job, and a brief description is included HERE, and in context of other issues, so it becomes clear how it works (or not!) http://www.historynet.com/us-torpedo-tr ... war-ii.htm

[phylo_roadking]

And here, on board HMS Alliaance, is a sectioned Mark VIII...and right at the left hand side of the pic we can see the "depth mechanism"!

http://webberswarships.ca/styled-13/fil ... k-half.png

As you can see, the adjustment was accessible from outside the torpedo so that the depth could be set. And from the pic in the post above it looks like the adjuster was covered by an oval-shaped screwed down plate. I know the Americans' WWII torpedos had an adjuster dial gauge on the outside of the torpedo tube in a sub where the running depth could be set on the depth adjuster inside the torpedo - but I don't know if the British torpedos had an equivalent...

But the depth mechanism was adjusted by inserting a square socket head into the square slot you can see to the right of the marked dial...



...and it looks indeed as if it could be done from outside the torpedo without unscrewing the plate. It appears to be the square socket hole on an (everso-slightly) different colour of oval plate in the airlaunched torpedo sitting ready for loading onto a Beaufort -



It looks like whoever set the running depth knew how many turns of the socket worked via the geared adjuster to set the pointer to the depth required on the marked dial.

The figures we can see on the topmost face of the dial go from 28 feet up to 42 feet; the question is...round on the other side of the marked wheel, at what setting do the numbers start, and at what number do they end...

[Andy H]

Hi

Its my general understanding that any torpedo can be set at 0 feet for its running depth.

It wasn't usually set as such, because of the risk of the torpedo porpoising/breaching Which obviously gives the potential
target a visual warning and also the porpoising/breaching can affect the direction of the torpedo, especially in rougher weather!

Regards

Andy H

[phylo_roadking]

Its my general understanding that any torpedo can be set at 0 feet for its running depth.

We'd know for certain if we could find a manual on the MkVIII and later and find out the exact procedure for setting it, and any exploded views/diagrams There's a couple of American manuals reproduced on the Internet, but no RN ones.

[Knouterer]

From a description of the Taranto attack:

"The Torpedoes
The standard torpedo for the first half of WW2 was the 18 inch Mark XII weighing 1,548 lbs with a warhead of 388 pounds of TNT. The maximum range of the Mark XII was 1,500 yards at 40 knots and 3,500 yards at 27 knots.

The torpedoes used for Operation Judgement were fitted with a duplex pistol (contact and proximity) detonator, and were set to remain armed at the end of their run. This is the first time the duplex pistol was used in the Mediterranean. The torpedoes were set to run at 27 knots at a depth of 33 feet. The minimum distance to launch was 300 yards from the target, and only contact with the water was needed to start the motor running.

These depth and speed settings were obtained from the experience gained from the torpedoing of the Richelieu at Dakar. There, the water depth was 42ft, the torpedoes set to run at 40 knots at a depth of 38ft. Both these settings were too high for the Mar Grande where the water depth was only 40ft, so the torpedoes were adjusted to 27 knots at 33ft.

The torpedo was modified for launching in shallow water by fitting an ‘air tail’, which added vertical planes to the ends of enlarged horizontal fins to improve its stability through the air so that it entered the water cleanly at the correct angle to run true. This prevented the torpedo diving too deeply before attaining its running depth; an essential requirement when launching in shallow waters. But testing had shown that, even with this ‘air tail’, the torpedo’s excessive dive beyond depth setting was 18ft when set to 40 knots, and at 27 knots it was 6ft. But 6ft was still too much for the shallow (40ft) waters of Taranto.

To eliminate entirely the excessive dive, each torpedo was connected to the launching aircraft by a spool of fine wire, the length and breaking strain of which was precisely calculated. After releasing the torpedo, the pilot had to hold the aircraft straight and level for five seconds while the wire unwound and the torpedo stabilised. When it had completely unwound, the wire came off spool, the torpedo continued independently and the pilot could make his getaway.

All this required the torpedo to be launched at low speed, at low altitude in level flight, a requirement that made the Swordfish the ideal aircraft to deliver it."

In a Sealion scenario, I don't think the Swordfishes, Albacores and Beauforts of the FAA and Coastal Comand would bother with the barges - which by the way were all made of steel and not wood - but would concentrate their attacks on the transports, of which there were 150+, of all sizes up to about 10,000 GRT. These would anchor offshore in about 75 to 100 feet of water, roughly, which should be ample for a torpedo attack. And considering that unloading these ships (into barges used as lighters) would take at least two days, there would be ample time for one or more attempts.

[Knouterer]

Even apart from Taranto, the “stringbags” were pretty effective against ships at anchor in 1940.

On the 5th of July, nine Swordfish of 813 Squadron from HMS Eagle – on this occasion starting from the airfield at Sidi Barrani – attacked Tobruk. They sank the destroyer Zeffiro (ammunition store exploded), and the freighter Manzoni (3,955 tons). The Liguria (15,134 tons) and the Serenitas (5,171 tons) were hit and left stranded, to be refloated by the British a few months later when the port fell into their hands. Not a bad bag for 9 torpedoes.

This feat was repeated on 20 July by nine other Swordfish from 824 Squadron, also from Eagle and also flying from Sidi Barrani. Two 1,715-ton destroyers, Nembo and Ostro, were sunk, while the 2,333-ton cargo vessel Sereno was left damaged and stranded to join the ships that would be recovered later by the British. Claims were also submitted for hits on a second merchant vessel and an oiler.

And out at sea, on 22 August in the Gulf of Bomba the submarine Iride (700 tons) was spotted on the surface while embarking four SLC underwater assault craft (“human torpedoes”) from the depot ship Monte Gargano. The intention was to attack Alexandria. Three Swordfish from Eagle attacked and sank the Iride, which broke in half with only five crewmen surviving, and the depot ship as well. The third torpedo passed underneath the torpedo-boat Calipso, which escaped thanks to its shallow draught.

(Source: Cristopher Shores et al., A History of the Mediterranean Air War 1940-1945, Volume 1)

[Natter]

What depth deep torpedoes run at? Where they adjustable?

For the british Mk VIII variants mentioned above, depthsetting was 0-44 feet.

I have attached some drawings of the Mk VII** depthmechanism - from a RNoN manual (I can provide better quality and/or translations if needed).
The construction is very similar to most other torpedoes at the time: A combination of a hydrostatic piston (controlling depth) and pendulum (controlling pitch/angle of attack) working on the rudders via a servoengine.

The depthsetting was adjusted by tensioning of the spring working against the hydrostatic pressure.

The tactical use/"policy" of depthsettings would vary, and normally would be described in a manual. Both the type of target, seastate and of course wether to use combined or impact only function would decide which setting to use.
When using an impact pistol, 2-3m (6-9 feet) would be a normal/typical depthsetting.

Where british torpedo pistols contact or magnetic?

Depending on type. The CCR pistol used in the Mk VIII's was a combined magnetic/impact pistol with two settings: Combined function or impact only.

Its my general understanding that any torpedo can be set at 0 feet for its running depth.

No, it's not the case for all torpedoes. It would vary both due to the design of the depthmechanism, and the type/purpose of the torpedo itself (mainly governed by the pistol). For instance, the british Mk IX had a minimum depthsetting of 6 feet.

[Knouterer]

To give some impression of the targets, here are a couple of the freighters of the Rotterdam convoy, the RO11 Alkaid (5,483 GRT; rated to carry 550 men, 200 horses and 97 vehicles) and the RO 12 Damsterdijk (10,155 GRT; similar Drechtdijk was rated to carry 2,500 men, 305 horses, 127 vehicles), taken from Volume 7 of Gröner et al., Die deutschen Kriegsschiffe 1815-1945.
Alkaid has a platform for a single 20 mm gun on the bow and a machine gun at the stern, while Damsterdijk has a platform for a single 20 mm at the stern.
In so far as can be made out from Gröner – it is mostly not so clear what armament was installed when – and from photos and other sources, one 20 mm gun seems to have been about average for the Sealion transporters at the end of Sept. Some carried more, many were as yet unarmed. Only about half a dozen ships carried anything bigger (37/75/88 mm).

[Natter]

As you can see, the adjustment was accessible from outside the torpedo so that the depth could be set. And from the pic in the post above it looks like the adjuster was covered by an oval-shaped screwed down plate.

...and it looks indeed as if it could be done from outside the torpedo without unscrewing the plate. It appears to be the square socket hole on an (everso-slightly) different colour of oval plate in the airlaunched torpedo sitting ready for loading onto a Beaufort

All adjustments on the torpedo (depth-, speed, distance etc) are available through openings in the hull.
I don't have a very good photo of the british Mk VIII, but at least you can see the mechansim as it appears on the torpedo in the attached photo.

I know the Americans' WWII torpedos had an adjuster dial gauge on the outside of the torpedo tube in a sub where the running depth could be set on the depth adjuster inside the torpedo - but I don't know if the British torpedos had an equivalent...

This was a common feature in all navies, although I don't know the details of the british. Anyway: It's a feature of the torpedotube, not the torpedo itself.
Many torpedobombers would also have a system making it possible to adjust some settings of the torpedo while airborne.

[phylo_roadking]

In a Sealion scenario, I don't think the Swordfishes, Albacores and Beauforts of the FAA and Coastal Comand would bother with the barges - which by the way were all made of steel and not wood - but would concentrate their attacks on the transports, of which there were 150+, of all sizes up to about 10,000 GRT. These would anchor offshore in about 75 to 100 feet of water, roughly, which should be ample for a torpedo attack. And considering that unloading these ships (into barges used as lighters) would take at least two days, there would be ample time for one or more attempts.

Ample time for one or more attempts...depending on the attrition suffered in the FIRST attempt...which I presume you're going to have them make in daylight, so they can tell the ships from the larger barges...

Oh - and given that they're going to be surrounded by many and various barges - loading, or unloaded and waiting - not to mention many and various smaller escorts and V-P boats...any attackers are going to have "clear shots" at them?

... and the Luftwaffe won't of course object to their being there in daylight...

[Knouterer]

Considering that the Luftwaffe was unable - or unwilling - to guarantee fighter cover over the beaches for more than about 15 minutes in the hour*, they certainly would have had a fighting chance of getting through, particularly if the RAF managed to coordinate attacks.

*At least, that was their position during a "Planspiel" with A.O.K. 9 on 24.9.1940.

[pugsville]

There been enough sealion threads I was just after some technical information and thanks guys it has been very informative. I think were should not degenerate in general sealion talk, start another thread (I enjoy those threads ) but I would like to remain fairly narrow on technical side here. My general questions have been mostly very well answered and I thank everyone for their information,

[Knouterer]

As regards the airlaunched 18in torpedoes, according to John Campbell, Naval Weapons of WWII, page 83, the original Duplex CR pistol used on those torps was unreliable and finally abandoned at the end of 1943. Against degaussed ships, it only worked if it passed no more than 2-3 feet under the ship, and if the torp was deviated sharply, prematures were caused by the earth's magnetic field.
Its replacement (compensated coil rod or CCR with amplifier) was more sensitive and functioned at 6-10 feet below the hull.