Submarines near to or on the surface were an obvious target for attack. The development of a crude underwater listening device, therefore, was of huge significance for a submarines crew.
The Fessenden oscillator, developed by Reginald Fessenden, below left, was first produced in 1915 and it allowed submarines to give and receive messages and also to detect ships while the submarines stayed submerged. A heavy diaphragm operated underwater by an electric current made it possible to send Morse code messages for up to 30 miles.
However, the Fessenden oscillators were non-directional so any ship could pick up the messages! Also the clarity of any message being received by the submarine was masked by engine noise or by the sound shadow cast by the submarine. The sound wave produced by the oscillator also varied depending on the density of the water – dense water impeded the motion of sound waves and, therefore, limited the distance they travelled.
Submarine wirelesses were constantly improved throughout the war and a major development was the invention of the telescopic masts. These allowed a submarine to surface and crash dive without having to send out crewmen to dismantle the mast in an emergency. The mast could be raised and lowered by compressed air and the lowering could be done underwater.
The invention of the gyro compass was invaluable to a submarine’s captain. Prior to this, navigation had been notoriously difficult. The gyro compass showed a true direction of travel at all times (in theory!). The compasses fitted to British submarines could detect a lag of ¼º thus enabling a correct course to be steered at all times. In 1914, the 'US Naval Proceedings' stated that a 2º lag represented one mile out of course for every thirty miles travelled – a considerable distance for a submarine. However, the gyro compass was not foolproof. Rough seas could upset its delicate mechanism.
|“They (gyro compasses) are awfully fussy creatures, harder to understand and manage than a women….we called them the ‘navigator’s nightmare’. (W G Carr)|
During the war, Britain invented three new types of torpedo.
1) One was powered by oxygen. Torpedoes powered by compressed air left a telltale wake in the water and gave a warning to a target. Oxygen is soluble in water and left no telltale wake.
2) Another was a circling torpedo. It did as its name implied. Once the torpedo had reached a pre-set distance, it circled – the theory being that if it had missed its principal target, it might hit another.
3) The third development was an acoustic or magnetic torpedo that was attracted to the noise made by a ship’s propellers or to its metal hull. This torpedo was of little use in World War One but it was to leave its mark in World War Two.