Operation Tunnel was a set-piece operation controlled by CinC Plymouth that was activated when intelligence or reconnaisance indicated that the Germans would be running a convoy along the French coast between Brest and St.Malo. There were no forces specifically allocated to it nor preparations made for it. CinC Plymouth detailed whatever ships he had available and tactical planning and control was left to whoever might be Senior Officer. Some continuity was provided by the Hunt class destroyers of the local 15th Destroyer Flotilla but their lack of speed and armament lessened their value. The operation was invariably activated with a mixed bag of ships with widely different capabilities few of whom had ever worked together before.
The Germans gave their merchant ships proceeding along the French coast strong escorts of at least four Elbing Class destroyers who worked together as a team plus a close escort of as many large M Class minesweepers as available. An important ship or convoy would also be supported by E boats. The Germans had an excellent radar chain along the coast and the liaison between this and their ships was good. There were several shore batteries with guns of ranges out to 15 miles. The Germans also had the advantage that they could time the sailing of convoys to make the best of light and weather conditions. Their tactics if opposed would be to draw the attacking force away from the convoy while this withdrew close to the coast. If faced with a close quarters situation they fired a full salvo of torpedoes before withdrawing at high speed.
The opposing forces on 21st October 1943
The British forces detailed were:-
Charybdis. An AA cruiser of 33 knots, eight 4.5" guns and a heavy close range AA armament.
Grenville and Rocket. Fleet destroyers of 36 knots with four 4.7" guns and eight torpedo tubes.
Limbourne,Talybont, Wensleydale and Stevenstone. Hunt Class destroyers of 27 knots, four 4" guns and two torpedo tubes.
Charybdis had never operated before as a surface force strike leader. Her entire life had been spent in providing heavy AA support mainly in the Mediterranean. She had very little experience or practice at surface actions. Her armament was designed to combat air attack and was smaller than that carried by some of the destroyers. She was not the right type of cruiser for the rough and tumble of a night action.
The two Fleet destroyers were armed almost identically to the T Class (Elbings) which the Germans used in this operation. They both had experience of night fighting in these waters.
The Hunts came from two different flotillas and the Senior Destroyer Officer in Limbourne had only joined his ship a few days before and did not know the other Commanding Officers. He was only able to attend at the end of the pre-sailing conference and had the sketchiest idea of the senior officer in Charybdis' intentions for the operation.
The German forces were:-
5 T Class(Elbings) of same capabilities as British Fleet destroyers all from the same flotilla.
6 M Class large minesweepers.
2 V Class patrol vessels fitted with radar, all as the close escort to:-
Munsterland a merchant ship whose safe arrival at Cherbourg was of some importance.
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