Actually, the site about U-47 linked earlier in this thread mentiones as much:
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Adorned with a makeshift conning tower emblem mocking the British Prime Minister Neville Chamberlain and armed with a full complement of the new G7e electric wakeless torpedoes, U-47 gently moved out from its base at Kiel on 8 October. Prien took a carefully-considered route to the Orkneys - lying on the bottom during daytime and keeping radio silence. The mission had been planned with the highest level of security, to the point where Dönitz had transmitted the details to Raeder by word of mouth, and by 4 October all other U-boats operating around the Orkneys had been withdrawn from the area. As Prien and his crew slowly made their way towards their target, it is highly likely those in the higher German chain of command were oblivious to the monumental task that had been set in motion.
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http://www.u47.org/english/u47_sca.asp
* U-boat.net seems to back it up:
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12:58...Impact firing. The boat lurched as one, two, three ton-and-a-half G7e torpedoes went overboard on blasts of compressed air, electric motors winding up, accelerating toward 30 knots. U-47’s hydrophone operator called, "Torpedoes on their way."
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http://www.uboat.net/ops/scapa_flow.htm