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British estimation of U-boat equipment October 1939

Discussion in 'Submarines and ASW Technology' started by Liberator, Mar 21, 2015.

  1. Liberator

    Liberator Ace

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    Thought this would be of interest.

    British estimation of U-boat equipment October 1939

    Taken from The Anti-submarine Division Of The Naval Staff - October 1939



    Miscellaneous information about U-Boats


    (1) German torpedoes

    According to prisoners of war, a highly efficient torpedo known as the " E " torpedo, which is electric, is in use in the German Navy. These torpedoes can be set to run at any depth up to 30 feet. They leave no tracks and have magnetic pistols. Though the informant claimed they have a speed of 50 knots, it is considered doubtful if their speed actually exceeds 30 knots.
    Further evidence of the existence of such torpedoes is obviously hard to obtain, seeing that it is trackless. Apparently, however, the Germans are using some form of heater torpedo as well, for very clear tracks have been reported by numerous ships. The Captain of " U.42 " stated that the German magnetic pistol was known to be unsatisfactory, but that it had been modified and was now very good (this may be incorrect).

    (2) German anti-submarine devices

    The Captain of the " U.42 " described the sound of our asdics as being " tick-­tick-tick," not a musical note. As soon as he was hunted he went in the control room and listened on his headphones. He stated he could tell more or less when an attack started and he continually altered course and tried to escape.
    It is interesting to note that when he arrived aboard H.M.S. " Imogen," he asked, " Are you fitted with asdic, I mean ping-ping-ping ? " One of the German petty officers, seeing a telegraphist wearing headphones at the entrance to the W/T office, said, " Are you the ping man ? Your ping very good." This petty officer, however, could not understand how they could have been attacked with such accuracy, because, as he stated, the " U.42 " had stopped engines for the attack. In general, the executive officers of " U.42 " seemed to have realised that the odds against them were heavy. Apparently our anti-submarine tactics have been very closely investigated from evidence of U-Boats which have been attacked and which subsequently have returned to Germany.
    Reports have been received from a number of our submarines on patrol in the North Sea that they have heard grunting sounds. It is not known what these noises are, and it is suggested that they may be due to natural causes, as noises were also heard in the last war, but it is by no means certain that they are the same.

    (3) German mines

    Further evidence has come to light about the mines which are being laid by German submarines. A prisoner-of-war stated that the mines are of a " bottom " type and remain married to the sinker until they are released by the magnetic effect of a ship passing over them. The mine is of a non-contact type, but it is not known if it fires hydrostatically on reaching a certain depth or has a form of magnetic relay inside it of the same type as our " M " mine. It might also have a delayed detonator.
    There are obviously limitations to such mines. They must be laid in water shallow enough to allow the ship's magnetism to operate the delicate relays. It is impossible to make these too sensitive or else a magnetic storm would cause the mines to detonate.
    Mines once laid cannot easily be cleared. A magnetic sweep was tried in Swansea Bay, but only exploded one mine. It is a laborious process. According to prisoners, the Germans have incorporated a deadening device in the mines so that they are inoperative after a certain period, given variously as 6 and 12 weeks. This, of course, renders it unnecessary to clear the mines. Vigorous steps are being taken to counter the danger of these mines.
    Submarines are apparently minelaying when submerged, by using compressed air to discharge the mines. It is probably done through the torpedo tubes.

    (4)Personnel

    From the evidence of prisoners it appears that the attitude towards sinking merchant ships is slowly changing. The Captain of " U.42 " thought it was madness for a U-Boat to fire a warning shot and allow the crew to take to the boats, as the ship invariably signals destroyers by W/T and will return the fire if she is armed. The only thing to do, he thought, is to torpedo a ship without warning.
    Apparently, losses of German U-Boats are not published in Germany. The Captain of " U.42 " was astonished to hear that the crews of " U.39 " and " U.27 " are prisoners. He knew, of course, that the submarines were overdue and probably lost, but he thought there would be no survivors. In one conversation, he said he was prepared to put the figure of U-Boat losses as high as 27, but that " a large number of our boats, although attacked, have returned." This high estimate of losses may well have been due to a desire to flatter his interrogators.

    (5) German W/T procedure

    The following procedure is used for communication between Germany and U-Boats. Every hour, Kiel, the control station, transmits, making pauses after each message. U-Boat transmissions are made during the pauses on the same frequency and are immediately repeated back by Kiel. A four figure group which denotes the time of origin followed by a two figure group giving the day of the month, forms the beginning of the message and this is followed by two figure group which denotes how many groups there are in the message. Four letter groups are used in the text and at the end the first two groups are repeated. Forty groups is
    the average length of a message.
    A barred E followed by a group of three figures, which is made three times,
    is sometimes used in traffic between units at sea. The following frequencies are
    used :—

    Time, G.M.T. and Kilocycleslsecond.
    0001.......................... 8,400
    0100 ..........................5,660
    0200 ..........................8,400
    0300 ..........................5,660
    0400 ..........................8,400
    0500...........................8,610
    0600.......................... 8,400
    0700 ..........................8,610
    0800 .........................12,940
    0900......................... 8,610
    1000 .........................16,410
    1100 .........................8,610
    1200 .........................16,410
    1300 .........................8,610
    1400 ........................12,940
    1500........................ 8,610
    1600 .......................12,940
    1700........................ 8,610
    1800........................12,940
    1900 ........................8,610
    2000 ........................8,400
    2100 ........................8,610
    2200 ........................8,400
    2300........................ 5,660

    4,412 kc/s has been used on occasion when it was impossible to get through on 8,400 kc/s.
    The Germans seem to be unaware that we are able to D/F their high frequency transmission. Naturally, the results vary greatly according to the conditions, but they are providing reliable indications of the position and movements of German U-Boats.
     
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