Submarines

A movie preview I just saw showed depth charges being use against a WW2 sub. They looked like oil drums. How did they work? Do we still use them today? Also can a sub survive a tidal wave when at sea?

===m==(ô¿ô)==m===

They had (and still do) have pressure-sensitive detonators. Sort of like a blasting cap attached to a barometer, but adjusted for water pressure instead of air.
They could be roughly calibrated to discharge at a certain depth.
From what I’ve heard of such things there wer a LOT of duds, and the ocean floor is littered with these things. Pity the poor whale that finds one!

A ship would use sonar to estimate the sub’s depth, then the charges would be set. Fortunately for the ship, the accuracy didn’t need to be too precise, because the blast wave created by a UW explosion is destructive far beyond the range of an air explosion. Water being incompressible and all…

Oops, missed one! A sub can ride out a tidal wave as if it didn’t even exist. Provided, of course, that it is in really deep water at the time. A tsunami (proper name) doesn’t become a problem until the rising of the sea floor near land causes the water to lift higher and higher. So unless the sub is in dock it’s safe as can be.

Well, they’ll feel something on a sub, but deep water is where you want to be if a tsunami’s working your neighborhood - surface or submerged. You don’t want to be close enough to land for the wave’s amplitude to cause your vessel to contact less movable bodies.

I don’t know if we still have depth charges around that we’re ready to use. I’m sure we have some in some warehouse somewhere, but whether or not our fleets are carrying them around - I don’t know. However, we do (or rather, did, since I believe we stopped carrying them as well) have tactical nuclear “depth charges” to use at sea that wipe out anything within about a 5 mile radius underwater. A bit more efficient, if something of overkill and not very ecologically friendly. Still, it’s better than waiting for some Polaris sub to launch its nuclear arsenal at you.

“I guess one person can make a difference, although most of the time they probably shouldn’t.”

I’m sure some sort of guided (heat, sound, or metal seeking) torpedo or underwater missle has replaced the old depth triggered cans of the WWII era.

I saw that preview, too. The plot seems to revolve around the US navy trying to aquire an Enigma (or is it Ultra?) machine from the Germans by posing as a U-boat off the eastern seaboard. I thought the British had already gotten a machine through the Polish Resistance long before the US entered the war. Hollywood wouldn’t stoop so low as to rewrite history, would they? Naw.

Cute, but unrealistic. If a modern boomer (Typhoon class, Ohio class) is going to launch it’s missiles, it’s likely not going to be anywhere near a destroyer. Hunter/Killer subs are far more effective at tracking missile subs. It seems destroyers would generally be limited to protecting convoys and fleets. In a nuclear situation, you could take those targets out with a single long range nuke. The only time you’d use depth charges would be under conventional war conditions, and therefore you couldn’t use nukes. And in that case, modern torpedoes are much more effective.

Any Navy men care to confirm or deny?

Or Navy women for that matter…

(my apologies)

I don’t know when we “acquired” specific Engima machines, but they were changed as the war went on (extra wheels added). IIRC, the Wehrmacht and Kriegsmarine also used different codebooks for their daily Engima settings, so those would have been very valuable as well. Not to mention we were always willing to steal a little German submarine technology here and there…

Too lazy to find hard cites, but mrblue92 seems to have it:
fast subs and guided torpedoes have pretty much killed off the classic depth charge.

WWII subs were slow when submerged, and had to be surfaced to fire torpedoes. Destroyers could therefore catch up with a sub and rain DCs on it all day with no threat of reprisal.

Today, we’d rather drop a guided torpedo from a chopper than let a sub get close enough to lob a guided fish at our ships.

The US has nuclear depth charges and nuclear torpedoes, but they’re being phased out (might already be) as part of the elimination of theatre (tactical) nuclear arms. That also means no more backpack nukes for dams, howitzer nukes for tank and troop formations, etc.

It’s hard to beat The Federation of American Scientists for modern military info, and they’ve got plenty to say about anti-sub stuff. My favorite is the “torpedo mine,” which sits on the seafloor till it hears a sub, then spits a guided torpedo at it.

I lead a boring life of relative unimportance. Really.

Submarines have been able to fire torpedoes submerged since the turn of the Century.

Depth charges are pretty much obsolete; some countries still use them, usually dropped from helicopters. Modern U.S. anti-sub weapons include homing torpedoes, and ASROC, which is a homing torpedo boosted by a rocket for about five nautical miles.

ASROC formerly used the same launchers and rockets to boost nuclear depth charges (about 0.1 kilotons, IIRC) to about the same range. This weapons is one of the reasons so many U.S. vessels were banned from certain Allied ports (Australia and/or New Zealand?) which forbade nuclear weapons; not many of our ships carried nuclear depth charges, but we weren’t saying which did and which didn’t.

A U.S. destroyer, attached to an escort carrier group, did attack and capture a German U-Boat in the Atlantic. I think the specific plan was to get an Enigma machine. The Germans were forced to surface; they surrenderd and opened the sea-cocks to scuttle the vessel. Fast-moving Navy men then boarded the U-boat, closed the sea-cocks, and saved the boat. Anyway, it was the first enemy vessel captured on the high seas by the U.S. navy in a really long time (since the Spanish-American war?) It wasn’t the first info the Allies had on Enigma, but it was an important catch since I think it was the first working machine we had.

“A U.S. destroyer, attached to an escort carrier group, did attack and capture a German U-Boat in the Atlantic.”

U-505, which you can see at the Museum of Science and Industry in Chicago. You wait in line (and wait, and wait) then see a short film on the capture of the sub (actual Navy footage of the capture, IIRC) before you enter the submarine.

With how little room there is to move around, you realize that a sailor serving on a submarine of that era was halfway to being buried at sea just by being aboard.

I’m not sure if this is what the movie preview is based on, but it details the event I referred to in my last post (it actually doesn’t mention Enigma by name…): http://www.fransorb.com/cve60.htm

This one mentions Enigma: http://fn2.freenet.edmonton.ab.ca/
~jsavard/ro0204.htm
I didn’t want that link to be too long … take the space out right before “~jsa…”.

The preview is for this movie:

U-571

Plot Outline: World War II action drama about a U.S. Navy submarine captain on a risky mission to swipe a decoding device from a stranded German ship.

Now why would an Enigma machine need to be stolen from the Germans? I thought the British (with the help of mathematician Alan Turing) had managed to decode Enigma-coded messages.

Our ability to read codes was top, top secret - it did not necessarily filter down to the level of task force commanders. The assumption was that we could not. So grabbing a code machine or code book was obviously an extremely important thing to do. It was also extremely brave - not only was the sub sinking, but they had explosives aboard which could have been (but weren’t, in the panic) set to blow up the sub. After they captured that U-boat, we isolated the crew completely until the end of the war, not even letting the Red Cross know about them. We did not want the Nazis to know we had a sub and their documents and machines - because then they would simply change everything. Our codebreakers must have appreciated the documents and machine, but I suspect they would have been just as happy if the sub went to the bottom with the Enigma machine and code books.

Also, even though we were allies, the British and the Americans generally didn’t share much intelligence. The British codebreakers had been deciphering Enigma messages for a while before the Americans even knew they were able to.

Damn that Alan Turing bastard.

There is one safeguard known generally to the wise, which is an advantage and security to all, but especially to democracies as against despots. What is it? Distrust. – Demosthenes

Joe Cool

Well, some of that I said…

In fact, the Polish Army Intelligence division had started decoding ENIGMA coded messages as early as 1925! By the early 1930’s the Poles had succeeded in building some mechanical computers (bombes) which were capable of sifting through the prolog (the first characters of the encoded message, which announced the wheel settings); and by 1936 had passed most of this info (including a complete machine) on to the french and British intelligence services.The poor Poles never got the credit they deserved for this!

I neglected to mention that said tactical nuclear weapons were designed to be dropped by air (I believe helicopter), not dropped by a ship as a conventional depth charge would be. While this still involves getting the aircraft over the spot in question, at least you don’t have to have a ship right there and with a 5 mile radius, accuracy isn’t of the utmost importance.

“I guess one person can make a difference, although most of the time they probably shouldn’t.”

I knew we had talked about this before. From another thread, here’s the revelvant portion about nuclear anti-sub technology:

Jophiel, Correct. The Nuclear Depth charge would wipe out A) all subs in a several mile radius, B) all surface ships in a couple of mile radius (Nukes underwater are Nasty) and C) most likely the S-3B Viking that dropped it. This is because unless the bomb is dropped rather precisely, the S-3B won’t get far enough away before it goes off. It can’t climb fast enough, and the nuke can’t be dropped from height. Jim is rather happy that they aren’t considered tactical weapons anymore, and have been phased out of doctrine.

The thread in question can be found at http://boards.straightdope.com/ubb/Forum3/HTML/001833.html though it’s more about tactical nuclear warfare than submarines.

“I guess one person can make a difference, although most of the time they probably shouldn’t.”