Tuesday, March 9, 2010

Mines

Mine warfare has been around for well over a century. But first, a definition: I define a "mine" as "an explosive device triggered by the passage of a ship".

Mines actually go back a lot further than a century. There were attempts to make working mines in the 18th and early 19th centuries. The problem was how to trigger them, as before the invention of the percussion cap, the only practical way to detonate a mine was to attach it to a ship and light a fuse.[1] Even the invention of percussion caps did not make mines very feasible, as the firing mechanism had to be something that was both waterproof (black powder and water do not mix) and crushable (to fire the cap). Command-detonated mines were tried, but they had problems with water seeping in along the wires and disabling the charge.[2] Mines became practical when explosives less susceptible to moisture were developed.

There are three basic types of mines and three basic methods to place mines. The types are contact, pressure and magnetic (there are also hybrids, which can be both pressure and magnetic). The three methods of placement are bottom, moored and drifting.

Contact mines are the ones that you always see in old war movies: Big round iron or steel balls with something like 200lbs of high explosives. A ship or sub would contact it and have a hole blown in her side. Bottom contact mines required very shallow waters; they were most commonly used as an anti-landing craft defense. Drifting mines are heavily frowned on by the Hague Convention of 1907, but that has not prevented their being used.

Moored contact mines were typically laid from minelaying ships. They were rolled off the stern of the ship. The anchor section contained the cabling and the wheels for being rolled off. The cable would pay out to the desired length and anchor the mine.


Ideally, the length of the cable would be set so that the mine was submerged, both so that the mines were harder to avoid and that they would not be detonated by fishing boats and other small craft. Moored contact mines can be laid in very deep waters. It is possible to lay them so that the mine case is targeted towards submarines.

Magnetic mines are triggered by the passage of large chunks of metal, namely, ships and submarines. Pressure mines are triggered by the hydrodynamic pressure generated by a passing ship. These mines can be very sophisticated and may include counters so not just the first ship to pass by will trigger them. More specialized are acoustic mines, which will activate on the acoustic signature of a particular class of ship. There was development of mines which incorporated homing torpedoes, the USN version was called CAPTOR.

Mines were first laid by specialized ships, but now are laid primarily by aircraft, at least for USN usage. They can be laid by submarine, but that requires cutting into the torpedo load, which submariners hate to do. When laid by aircraft, an enemy will attempt to spot the splashes to aid in demining. As a result, it is common practice to drop mine cases that are filled with cement as dummies. This also works because few ship captains are willing to try a minefield.[3]

Mines could be used defensively (to keep opponents away) and offensively (the "North Sea Mine Barrage"). The threat of mines was often enough to prevent a naval force from moving into an area.

I will cover mine countermeasures in another post.
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[1] The modern equivalent is a "limpet mine", which is attached by a frogman.

[2] Similar issues bedeviled the first undersea telegraph cables.

[3] I was told that when the Navy mined Haiphong Harbor, most of them were dummies. That might be bullshit, though, as it was a naval aviator who told me and they are famous for being bullshit artists.

9 comments:

Jimh. said...

To hear Naval Aviators talk they are the best of the best of the best. Especially when describing the difference between themselves and a USAF pilot.

That is very interesting. I knew some, but you always add to my knowledge! Thanks EBM!

steveeas said...

Funny. Spent years walking past MSO's in port. Never met anyone from that community; peers or otherwise.

steve osc ret

PhysioProf said...

Mines kick motherfucking ass! KABLOOIE!!!!!!

I will cover mine countermeasures in another post.

I can't wait!

stephen said...

I was on a sweep in the late 70's, early 80's and was told the same thing about Haiphong harbor by one of the guys cleared it.

One of the problems with MCM is that on sonar a 50 gal drum would return the same echo as a mine. We would class objects as "mine like", but the only positive ID was by diver.

So if you really wanted to fornicate with some one, you would drop a lot of trash with your mines and make them look at each and every little piece...this could take awhile and meanwhile you are spreading more mines and trash.

Mine warfare is a neglected part of the Navy, not glamourous enough I suppose. Of course, I could bottle up Norfolk harbor with a few bottom layers with a long time delay and high ship count among all the garbage on the bottom. They would be a perfect terrorist weapon as all you would need would be a small boat to drop them off in and some of the simpler types would be great for low tech manufacturing. Remember the tanker war in the Gulf....

We actually swept a moored mine off the Marine exercise area in SOCAL the early 80's. Turned out to be a practice mine left from an earlier time. Had to clean out some pants after that one.....

Don't forget to mention the guinea pig sweep....

stephen said...

The sweep navy: In the late 70's the sweep navy consisted of 100% reserve ships.

This means you normally had 1/2 to 1/3 the crew and about 40% of the money. So the only time we were not port and re-port was when the reserves were doing their weekend or two weeks.

These ships were about 130' on deck, 30' of beam, 10' of draft. They were round bottomed. They made of of wood and had systems on them to deqauss them (demagnetize). We also degaussed at special facilities. Propulsion was 4 diesels with CRP's-controllable reversible pitch propellers. Parts could be a bitch.

They also had a really big generator set-this was to power up the magtail-a big ass electrical cable we would put in the water to spoof the signature of a larger ship. I think we had about 1500 ft of this. We also carried acoustical devices and mechanical gear.

They were very manuverable, but in any kind of weather the ride sucked because you bobbed like a damn cork. I have literally seen an entire crew with the exception of the watch, flat on their backs with seasickness. The watch was busily throwing up in plastic bags. One day of this was bad enough-five or six was real hell. I remember we delayed a port call by one day just to clean the puke off the ship.

My sweep had a walloping top speed of about 14 knots, but could not sustain it for long. Ten knots or so was normal. Took a while to get anyplace.

stephen said...

Sweeps were very seaworthy little buggers, even if they were a rough ride. Damage control-fires in particular-were always a worry. The USS FORCE, MSO 445, was lost off of Guam due to fire. Fuel oil hit a hot turbo charger and that was it. Scuttlebut was that it was 10 minutes between GQ and abandon ship. We took firefighting seriously.

stephen said...

Airdales and MCM: The airdales would tow either a MOP (Magnetic Orange Pipe) or a special MCM rig that they had-mainly acoustic-magnetic -in the water. Needless to say they DID NOT like this, being in a confined op area around a bunch ships and having to stay at low altitude to tow their gear in the water.

They were mostly used for precursor sweeps to clear the lanes to the beach. They could NOT be trusted to stay where the hell they were supposed to and we were constantly thinking we would get slammed by the MOP.

stephen said...

To continue

Back in the day (before GPS)you had two issues that were pretty difficult to resolve. One was finding the mine itself. Related to this was the concept of returnablity. Once you had found something , you may be required to return to it later.

This could be a real issue due to the nav gear of the day-radar, DRT and chart. The sonar system was short range and water conditions would vary, so if you were trying to return to a promising object to sweep it, you had to rely on luck more than anything. Even if your nav fix showed you were dead on, you were still relying on luck more than anything.

Another issue was the gear itself. If we had all our gear out to the full extent, you had to maintain a certain speed to keep the gear strung out correctly, and to allow the depressors and otters to do their job. An engineering casualty could cause your gear to run over itself and foul. It could also cause you to ground your gear and tangle it up on the bottom. This was regarded as a bad thing by the fantail crew where the gear was deployed from.

One of the things the BMs and other guys on the fantail had to keep an eye on was the tensionometer. Now the forces involved in towing a few hundred to 1200 ft of heavy gear and sweep wire in deep water were pretty considerable and the tensionometer
kept the guys safe-once it hit a certain reading, it "CLEAR THE FANTAIL" because after that you were going to be approaching the limits of the cable and if either one broke, you did not want to be around.

There were two kinds of cable involved, both were wire rope at least 1 inch thick if I remember correctly. The sweep wire had a special strand woven through it that was extra hard. This was so that any mooring cables rubbing against it would get cut. The rest of the gear was strung on ordinary steel cable.

Comrade E.B. Misfit said...

Stephen, if you want to assemble all of that stuff into one e-mail and amplify it as you desire, and you send it to me (stinsongal at gmail dahht com), I'll be honored to post it as a guest post with full credit to you.