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[Page 40]
but they proved of little use either acting independently or in concert with the "fish".
The bi-directional was a different affair altogether. A short crane was fitted on the forecastle abreast the chart house. From the end of this crane a metal bar containing three sheaves was suspended at right angles. Through the two wing sheaves steadying lines were placed supporting the weight of the hydrophone. Through the centre sheave was placed the insulated wire cable connecting the hydrophone with the silence chamber and the listener therein. The microphones of this particular type of hydrophone were contained in a flat circular gun-metal bottle about 15 inches in circumference. In the centre, on either side of the bottle, were fitted two thin white metal plates or discs. These discs were in direct contact with the microphone within. The method of operation was this. All way was taken off the ship. All auxiliary machinery including the dynamo was stopped and the hydrophone lowered over the side to a depth of about twenty feet. No one was allowed to move about the decks or talk while the listening period was on. The operator, with an ordinary pair of receivers over his ears, listened in the silence cabinet while, with a small handle connected with a Bowden wire, he turned the hydrophone in any direction he wished.
Considerable Danger
It can easily be understood that in a narrow sea such as the Adriatic the home of practically all the submarines operating in the Mediterranean, these listening periods were fraught with no small amount of danger. Given a Fritz lobbed up within range of you while you were thus stopped, nothing could possibly prevent you from being torpedoed before you could get manouvring way on your vessel again. It took roughtly 60 secs. to come to a dead standstill after the engines had ceased going ahead and were turned astern and about 90 secs. to work up from that condition to, say, 8 knots. Either period was sufficient for a moderately skilful Fritz to get two or even three torpedoes home. Naturally we took every precaution whilst using this bi-directional hydrophone. Guns were all loaded and the crews closed up, the guns being trained in either beam, ahead and astern. Additional look-outs were placed