Mine laying by Submarine, especially in shipping lanes at entrances to major ports was most effective. Japan had 4 mine laying Submarines, each carrying 42 mines to be discharged through a stern tube. One of these Submarines, 1-124, was sunk off Darwin in January, 1942, by the U.S.S. "Edsall," and Australian Mine Sweepers, "Deloraine," "Lithgow," and "Katoomba." This Submarine was the first Japanese boat to be sunk by the RA N. Japanese Submarines 1-121, and 1-122, laid mines off Singapore at the time their Carriers were approaching Pearl Harbour.
[ click for enlarged photograph ]
The German Magetic Mine
This mine was triggered by the magnetic effect of a ship passing over it. This led to the counter measures of the LL electric sweep, towed by Mine Sweepers to explode the mines astern of the Sweeper, and degaussing for surface ships.
I recall H.M.A.S. "Australia," having her degaussing cable fitted at Simonstown Dockyard in South Africa. in June 1940, and notes from my Midshipman's Journal, dated 20 th. of June, read, "In the degaussing cable, 23 miles of wire were used, in all, there are 3 coils, one round the whole ship, one round the fore part, and a third round the after part of the ship. The current for this set up is taken from the Port crane, which may not be used when the degaussing cable is charged .
The objective of this cable is to set up a magnetic force which opposes that of the ship, in fact, to achieve a neutral state. Magnetic Mines rely on a magnetic force to attract a needle, to close a circuit and activitate the Mine. If a neutral magnetic state is achieved in the ship, then the Magnetic Mine is rendered harmless. As the ship proceeds North or South of the Magnetic Equator, the electric current direction needs to be reversed when passing from one hemisphere to the other."
(a) The Hydrophone
Used by Submarines to locate Convoys or Escorts, by the sounds emitted from their machinery and propellors. Vice Admiral Uretton (he was a most experienced escort Commander himself) indicates, "U-Boats were fitted with excellent hydrophones which "listened" for propellor noises. When dived to about 100 feet, the hydrophones gave remarkable results, detecting Convoys and large Warships up to 50 miles away. They were equally useful by day or at night ,so noise rather than smoke was probably the main giveaway of a Convoy's course and speed"
When used in this context, the hydrophones may well be termed an offensive weapon, but it found a great deal of use when the U-Boat was trying to evade an attacking Escort.
(b) The Schnorchel or Schnorkel
Both Allied Surface Ships and Aircraft, fitted with effective radar forced U-Boat Captains to remain submerged for as long as possible, when necessity made them come to the surface at night to recharge their batteries, they became most vulnerable. Thus the "Schnorchel," had its genesis, it consisted of a single casing, hinged to the deck just foreward of the bridge.
Two tubes were located inside this casing. When the "Schnorchel," was in the raised position, the top of the intake tube and the periscope were level. The exhaust tube, a little shorter, discharged burnt gases downwards. The U-Boat had to come up to periscope depth with tIle "Schnorchel," up, and the diesels running.The Boat could then run at 3 to 4 knots, and charge her batteries simultaneously.
(c) Development of an Early Warning Radar Detector
The German Submarine Service was ill served by its Boffins. They failed to develop and supply an adequate search receiver capable of picking up Allied Aircraft's radar transmissious, and the U-Boats had been slaughtered in the Bay of Biscay by Allied Aircraft during July, 1943. The 80 cm "Gema Scanner," an adaptation, albeit a poor one, of Naval Gun Radar, saw service in 1944, then came "Hohentwiel," having a 43 cm. wave length was developed from a Luftwaffe set, and was able to detect an Aircraft up to a distance of 6 nautical miles.
Some what belatedly, the "Hagenuk" company was asked to produce a Radar detector. It was code named "Wanze," or "Bug," and came into service mid August, 1943. In the following November, it was superseded by "Wanze G2," which did not emit any radiation.
The "Naxos," search receiver, was the first that could locate 10cm. Radar, and in early 1944, a more sensitive detector "Fliege," (Fly) was supplied. Finally the "Mosquito," or "Mucke," which located 3cm. Radar emissions became available.
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