1. The submarines allocated to these flotillas involved somewhat of a “general post” in home waters. The details can be studied by comparing the dispositions in Appendices II and IV. Some submarines went straight on patrol without calling at Dundee.
2. The first five boats on the Obrestadt line were Seahorse, Starfish, Triumph, Sturgeon and Spearfish.
3. Ursula, Unity, Undine, L27, L26 and H32. This last submarine, the only H boat with asdics, was temporarily in the Sixth Flotilla until L23 completed refit.
4. Porpoise, Cachalot, Oswald, Osiris and Otway.
5. The third of this class, Thames, had returned to the United Kingdom for a major refit. Narwhal was refitting in the United Kingdom too. These two submarines with the boats at Malta and Gibraltar made up the thirteen promised by the Admiralty.
6. Regulus, Perseus, Phoenix and Rainbow.
7. The German Navy took up a number of trawlers for patrol duties, manned by skeleton naval parties as well as their peacetime crews. At this stage they had no detecting devices or armament and relied on their lookouts and the ram.
8. In fact the German U-boats had orders to operate in accordance with International Law and U30 was wrong to act as she did.
9. The splash of discharge should not have been visible if the tubes had been properly calibrated. The U class, however, had had difficulty with this problem on trials and had been accepted for service without it being fully solved. German records give no indication of a
second U-boat being in the vicinity. The second torpedo attack was probably at the retiring U35 as well.
10. It may seem strange that the whole flotilla was sent out on patrol together. No doubt this was done to try to close the exits to the Heligoland Bight at the most likely time for surface raiders to emerge.
11. It was usual after this accident to restrain submarines on patrol lines from attacking other submarines. In this case, Spearfish’s contact with a U-boat a week before in this area undoubtedly caused uncertainty.
12. U36 was one of five U-boats sent out into the North Sea to attack commerce in accordance with International Law.
13. Faster for the larger submarines and slower for the small ones.
14. Low buoyancy means that the main ballast tanks are partly flooded to help a rapid crash dive.
15. Between 4th and 17th September, four minelayers and six destroyers laid a total of 3879 mines and anti-sweeping devices in six operations.
16. The German hydrophones were undoubtedly better than anything developed by the British in the First World War. They worked best with the ship stopped but could obtain some results up to a speed of 6 knots or so and they were directional. They also had a primitive echo
ranging set that could only be used at slow speeds and was of short range. It found difficulty in picking out submarine echoes from false echoes and reverberations. it was not generally used for searching like the asdics. Initial contact and bearings were generally obtained
by hydrophone and the echo system was used for ranging when contact was obtained.
17. Seawolf believed that the cruiser was patrolling off Hirtshals. German ships had in fact been patrolling in the Skagerrak and Kattegat since 26th September to intercept and inspect merchant shipping.
18. U13 had been one of six U-boats sent to intercept units of the Home Fleet off the east coast of Scotland. The operation of a submarine with a trawler against U-boats dates from the First World War, when two U-boats were destroyed in this way. In these early operations,
a C-class submarine towed submerged by the trawler with communication by telephone. In the Second World War operations, the submarines simply accompanied the trawler, which pretended to be fishing. The hope was that a U-boat would surface to sink the trawler by gunfire and that an opportunity would occur for the submarine to torpedo her.
19. The Germans did succeed in luring the Humber Force of cruisers and destroyers into range of the Luftwaffe. Attacks by well over a hundred bombers, however, scored no hits.