Signals security aroused Dönitz's suspicions during the war. On 12 January 1942 German supply submarine "U-459" arrived 800 nautical miles west of Freetown, well clear of convoy lanes. It was scheduled to rendezvous with an Italian submarine, until intercepted by a warship. The German captain's report coincided with reports of a decrease in sightings and a period of tension between Dönitz and Raeder. The number of U-boats in the Atlantic, by logic, should have increased, not lowered the number of sightings and the reasons for this made Dönitz uneasy. Despite several investigations, the conclusion of the BdU staff was that "Engima" was impenetrable. His signals officer responded to the "U-459" incident with answers ranging from coincidence, direction finding to Italian treachery. General Erich Fellgiebel, Chief Signal Officer of Army High Command and of Supreme Command of Armed Forces ("Chef des Heeresnachrichtenwesens"), apparently concurred with Dönitz. He concluded that there was "convincing evidence" that, after an "exhaustive investigation" that the Allied codebreakers had been reading high level communications. Other departments in the navy downplayed or dismissed these concerns. They vaguely implied "some components" of Enigma had been compromised, but there was "no real basis for acute anxiety as regards any compromise of operational security."