[JScones]

One of the primary RN objectives early in the war was to increase the defences around the British Coast. To this end, an anti-U-boat mine barrier was constructed in the English Channel across the Straits of Dover. This was completed in October 1939 and resulted in three U-boat sinkings during October alone. Attention from *both* Britain and Germany then turned to mining the east coast of Britain. Germany was also having a go at mining the Channel.

Whilst Doenitz had pondered the continued use of the Channel during October (there's a few entries in his diary on the subject, including the detailing of some rules about passage and engagement), it wasn't until December that he finally decided to "give it up" as a passageway to the Atlantic. He wrote this in his diary on 4 December 1939...

"...Letters from captured members of her crew indicate that U 40 struck a mine. This is the first proof of mines in the Channel. Air reconnaissance of the Dover-Calais Straits has not so far been carried out. Buoys and lightships have been laid off the English coast, showing that minefields have been laid, but nothing certain is known of their position and type. I must now give up this route into the Atlantic; there must not be losses on passage. With so few boats, each loss means such a considerable reduction in strength that it outweighs the disadvantages of a long and fruitless passage. With regard to the boat's operations as such, I do not see any other way of conducting them if successes are not to decrease. It will be necessary to carry on in the same way as at present and accept the inevitable losses. It is only thus that the small U-boat arm, pitted against far superior forces, can hold its own as a part of the war as a whole."

Thus, all U-boats (rather than just a select few) commenced taking the "long way around" to the Atlantic.