German Submarine Warfare 1914-1918 in the Eyes - British Naval ...

traffic by the Royal Navy. This fact was obscured until the 1980s, when Britain
made the information public.
German diplomatic traffic was also deciphered and gave insight into strategy
and tactics. The most famous example is Zimmermann-telegram, in 1917. As
Britain had cut the undersea telegraphic cables at the beginning of the war,
Germany had to look for another way to communicate with its embassies in neutral
countries. Sweden transferred classified German diplomatic traffic as its own over
the Scandinavian cable network. But as London was the central hub for all
European cable networks and as nearly all networks were run by British companies,
this “Swedish-German line” was detected early and the messages deciphered with
the aid of the captured naval codes. The same thing happened to the W/T traffic
from Nauen to German embassies in Spain and the United States. Secret actions
like the shipping of wolfram ore from Spain to Germany by submarines, or the
landing of Sir Roger Casement in Ireland and other clandestine actions were
discovered in this way.
Other intelligence sources included some eight hundred submarine officers
and men who had become prisoners of war. They were a rich source of intelligence
about the tactics, the state of the German fleet, the status of shipbuilding, training
programs and other details affecting the Imperial Navy. Because the war played out
mostly in the relatively shallow coastal waters around the British Isles, sunken
submarines could be raised for close technical examination or inspected in situ by
divers. In this way, additional codebooks and a detailed knowledge of U-boat
design was obtained.
The Admiralty knew the numbers of submarines in service, their bases and
tactical units, the deployment schedule, crew morale and how many new submarine
orders had been placed. Unfortunately due to torturously slow intelligence
dissemination, commanders at sea got little benefit. Often, twelve or more hours
elapsed before destroyers arrived at a location where a U-boat had last been
spotted. 36 Consequently, only a handful of submarines were sunk as direct
consequence of deciphered W/T or D/F. 37 Deciphering played a more important
part in 1917/18 when it helped to redirect convoys from identified submarine
positions.
Aircraft support was equally ineffective. Aircraft were slow, relatively scarce
and had a limited range. Anti-submarine surface ships were equipped with an
imprecise a passive noise detection device, the hydrophone. Depth charges first
came into use in 1915/1916. In the first two war years, deck gunnery and ramming
were the chief submarine killers. Admiral Beatty could not have been more succinct
when he summed up the dilemma as “looking for a needle in a bundle of hay, and, when
you have found it, trying to strike it with another needle.” 38
36 Calculation example from: NA, ADM 116/3421, pp. 297- 298.
37 For an example see the stoy of U-154 in this book.
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