Depth Charges

[PhilB]

I`ve just watched "Run Silent, Run Deep" in which Clark Gable and Burt Lancaster take out a Jap destroyer with a bow shot. Several scenes were shown in which the submarine (or a model thereof!) gets depth charged. The DCs exploded within a few yards of the sub and the men inside stumbled about and the regulation bulb blew. A leak started and a crew member fixed it by a quick turn of a spanner. It struck me that DCs wouldn`t be much good if that`s all they did so presumably that`s not a realistic scene.

How far from a sub would a DC need to explode to cause fatal damage? Would WW1 subs be more vulnerable or were DCs then less effective? Phil B

[Chris Henschke]

http://www.de220.com/Armament/Depth%20Char...epthCharges.htm

http://www.1911encyclopedia.org/Submarine_Mines

[PhilB]

Thanks, Chris. Those references indicate that the explosion needed to be within 10 yards for a kill. Considering that the sub could be at any depth down to its limit, that seems a very difficult requirement! Phil B

[Michael Lowrey]

Phil,

In general anti-submarine warfare was less effective in WWI. Only 1 in 10 (or so) U-boats sunk in WWI were by taken out (in part or whole) by depth charges. There a couple reasons for that: depth charges hadn't even been invented when the war began, and until more than halfway through the war were scarce. And the depth charges of 1917 and 1918 were primative compared to those of WWII as was the ability to listen for submerges submarines. (Most succesful depth charge attacks in WWI involve a submarine surprised on the surface and depth charged at still shallow depth while trying to dive deep.)

Also note that WWI was more coastal than WWII, which tends to reduce one method of sinking submarines via depth charges — a sudden loss of trim and involuntarily going below crush depth. If you're in only 60 meters of water in the English Channel, the U-boat would hit the bottom and might yet be brought home. If the bottom isn't shallow enough when it losses control (as is usually the case on the open ocean), the boat simply is crushed by the preassure of water pushing down on it.

Best wishes,

Michael

[PhilB]

Probably a daft question, but what would happen to a shrapnel type explosion underwater? What kind of effective range would the projectiles have? What kind of range would a rifle bullet have underwater? Phil B

[Borys]

Ahoj!

I've read about HE shells for use against diving submarines, with special shape as not to tumble when they hit the water. Nothing about shrapnel, so I'd guess their usefullness to be nil.

Borys

[Justin Moretti]

QUOTE (Phil_B @ Jan 5 2007, 10:56 AM) <{POST_SNAPBACK}>

Probably a daft question, but what would happen to a shrapnel type explosion underwater?

What kind of effective range would the projectiles have?

What kind of range would a rifle bullet have underwater? Phil B

The effective range of (high velocity Spitzer) rifle bullets underwater is, I understand, in the order of a few yards (still having velocity to hurt a human). If we assume for argument's sake that a submarine hull is proof against rifle-calibre smallarms fire (it may not be, but must be more so than a human being), then shrapnel would not do much. Naval guns have approximately the same velocity as high-power rifles, e.g. around 3000fps for the final mark of 9.2in gun, and then you must allow for:

The shell slowing down as it flies downrange (probably not much) and a further drastic slowing as it enters the water.

The shrapnel balls are discharged forward with approximately the same velocity as the shell had when the charge goes off; all it does is fling them clear of the shell to allow dispersal; underwater this effect MAY be increased a little, BUT...

Shrapnel balls are round; their ballistic coefficient is godawful; the velocity would decay markedy.

A sphere is NOT the best shape for punching through metal, except maybe at velocities which are simply not achievable underwater using WW1 (or perhaps any) technology.

[healdav]

The subject of depth charges is a special subject that I can't say I am particularly expert in, but.....

When WW1 started there was pretty well no weapon that had been designed to be anti-submarine. In fact, there is a legend that the first sub ever to be damaged by a surface ship was hit by a sort of whale harpoon! Certainly, these sort of harpoons were issued for a time.

The problem at first was twofold.

There was no really effective sonar and the depth charges were time set, not hydrostatic.

So, the first sonar (to use the name) was not active, merely hydrophones. These were not really directional either - or at least not sophisticatedly so. Depth had to be estimated from the angle of the microphone.

As in WW2, depth charges were normally dropped over the stern. This had the disadvantage (to say the least) that as the ship ran over the position of the sub, the sound from it got lost in the noise of the ship's engines and propeller.

If he was able to do so, a sub's captain would be well advised to wait until the ship was more or less over him and then make a sharp left or right turn and get away before the noise had died down.

And, of course, the depth charges had to be time set so the rate of descent of the depth charge had to be estimated on top of the estimate of the deth of the sub. Water density could affect descent as could the water disturbance from the ship's propellers. Not a recipe for great accuracy.

Pressure fuses became available from 1916, but were only widely available from 1917. At least these exploded the charge at roughly the right depth. Of course, by WW2 ASDIC had come in and the depth and distance of the sub was available before the fuses were set.

Today, of course, depth charges are fired over the ship by mortar and so the sub can be 'held down' until the firing. This gives much better accuracy.

Surface launched torpedoes work quite differently.

Quite honestly, any sub captain who bow shot at an attacker would be asking for trouble (ramming, perhaps and a very difficult shot, especially if he was diving at the same time). Best left to Hollywood I would say.

The distance at which a depth charge would harm a sub varies directly with depth and position.

If it exploded above a sub at more or less maximum depth, the shock wave might put it below maximum and cause water pressure to cause damage. One exploded below the sub would push it up towards safety.

Two exploding close by and both below and above or on each side would cause the most damage. But they would need to be pretty close. The water tends to act as a protecting blanket at any sort of distance - see the reason for exploding the dambusters bombs against the dam walls, not a few metres from it.

I hope this is of help.

[Martin Bennitt]

see the reason for exploding the dambusters bombs against the dam walls, not a few metres from it.

The dambusters' bombs in fact were not conventional bombs at all but giant depth charges. Smaller versions were developed for anti-shipping use but never used.

From Wikipedia article on depth charges, referring to World War II: "Most U-boats sunk by depth charges were destroyed by damage accumulated from a long barrage rather than by a single carefully-aimed attack. Many survived hundreds of depth charge detonations over a period of many hours; U-427 survived 678 depth charge blasts aimed at her in April, 1945, though many (if not all) of these may have actually detonated nowhere near the target."

This, on the other hand is a totally different animal:

http://en.wikipedia.org/wiki/Nuclear_Depth_Bomb

cheers Martin B

[MartH]

Hello

There are some very interesing facts about this in Norman Friedmans book on the Design and Development of the Submarine. I will dig it out tonight.

One of the big successing in WW2 for the Operational Research Department was to get the airbourne dropped depth charges set to a shallower depth, they were exploding too deep below the half submerged U Boat. Hence U-boat sinkings went up, and it was a great sucess, though the tale has a cautionary note in it, about understandings ones sources. For years after this was used as one of the shining examples of OR in military use and the results used/applied to all subsequent U- boat sinking.

The early Secret homing airbourne dropped torpedoes where called MK41 or 42 Depth Charges as a ruse .. and other people included thier sinking in the analysis/results.

Regards

Mart

[PhilB]

The dambusters' bombs in fact were not conventional bombs at all but giant depth charges. Martin B

What`s the difference between a pressure fused bomb and a depth charge? Phil B