Boy-Ed possessed a copy of the secret British Admiralty code, which explained his frequent trips to Sayville. He knew--and Tirpitz's staff therefore knew--the position of any British vessel at sea which had occasion to utter any message into the air. But before he conceived a use for this code other than as a source of information, he decided to try out a code of his own.
He arranged with Berlin a word-system whose theory was popular with Germany throughout the earlier years of her secret war communication: under the guise of apparently harmless expressions of friendship, or grief, or simple business, were transmitted quite definite and specific secret meanings. A message addressed by wireless from the _Lusitania_ to a friend in England which read for example "Eager to see you. Much love" would scarcely arouse suspicion, especially as there was no word in it which might suggest military information. Yet in February, 1915, a message of that type was despatched from the eastward-bound _Lusitania_ to a British station; it was intercepted and interpreted by a German submarine commander in the "zone" nearby, who presently popped up in the ship's wake and fired a torpedo. His information was better than his aim. The _Lusitania_ dodged the steel shark, and fled to safety, her wireless informing the British naval world meanwhile of the presence of the U-boat.
The plotters had to reckon with her unequalled speed. The _Lusitania_ and her sister ship, the _Mauretania_, had each rather prided herself in the past on reducing the other's fresh, bright passage-record from Queenstown to New York--a record of four days and a few hours! The submarine of 1915 knew no such speed, and it was necessary, if the liner was to be torpedoed, to select out of the vastness of the ocean one little radius in which the submarine might lie in wait for a pot-shot. But just how?
Spies had reported that it was customary as the _Lusitania_ neared the Irish coast on her homeward voyage for her captain to query the British Admiralty for instructions as to where her convoy might be expected. They reported that under certain conditions German agents might be placed on board. And they reported that the wireless operator was susceptible to bribery. Those three facts formed the nucleus of the final plan.