Intelligence played an important role in the Battle of the Atlantic. In general, BdU intelligence was poor. Counter-intelligence was not much better. At the height of the battle in mid-1943 some 2,000 signals were sent from the 110 U-boats at sea. Radio traffic compromised his ciphers by giving the Allies more messages to work with. Furthermore, replies from the boats enabled the Allies to use High-frequency direction finding (HF/DF, called "Huff-Duff") to locate a U-boat using its radio, track it and attack it. The over-centralised command structure of BdU and its insistence on micro-managing every aspect of U-boat operations with endless signals provided the Allied navies with enormous intelligence. The enormous "paper chase" of materials operations pursued by Allied intelligence agencies was not thought possible by BdU. The Germans did not suspect the Allies had identified the codes broken by B-Dienst. Conversely, when Dönitz suspected the enemy had penetrated his own communications BdU's response was to suspect internal sabotage and reduce the number of the staff officers to the most reliable, exacerbating the problem of over-centralisation. In contrast to the Allies, the "Wehrmacht" was suspicious of civilian scientific advisors and generally distrusted outsiders. The Germans were never as open to new ideas or thinking of war in intelligence terms. According to one analyst BdU "lacked imagination and intellectual daring" in the naval war. These Allied advantages failed to avert heavy losses in the June 1940 May 1941 period, known to U-boat crews as the "First Happy Time." In June 1941, 68 ships were sunk in the North Atlantic () at a cost of four U-boats, but the German submarines would not eclipse that number for the remainder of the year. Just 10 transports were sunk in November and December 1941.