The Battle of Britain Five Months That Changed History, May—October 1940 by James Holland (z-lib.org).epub

destroying British merchant trade through the Channel. Although there
were just two flotillas of nine and seven boats each, the S-boats had scored
a number of victories during the Dunkirk evacuation, including the British
destroyer HMS Wakeful. Bobby Fimmen and S26 had also scored their first
victory when, in tandem with S23, they destroyed the French destroyer
Scirocco, in a daring night-time attack. The ship had sunk in minutes,
taking with her 480 soldiers.
With the fall of France, new opportunities had arisen. Because convoys
passing through the Straits of Dover could be better protected by day than
by night, the commander of S-boats, Korvettenkapitän Hans Bütow,
realized that convoys would thus often be passing west of the Isle of Wight
at night. This would provide great opportunities for his wooden-hulled S-
boats, which could speed over magnetic minefields, smash the convoys,
then speed back again. The ports of Cherbourg and Boulogne were ideal
bases from which to launch such attacks.
The 1st and 2nd Flotillas had reached Boulogne on 25 June, and three
S-boats from the 1st Flotilla, including Bobby Fimmen’s S26, had then
moved to Cherbourg three days later; the rest of the flotilla arrived on 1
July. Bütow believed his S-boats could wreak havoc on Allied shipping in
the Channel if they worked closely in tandem with VIII Fliegerkorps, which
was now based in Normandy. If von Richthofen’s Stukas and Me 110
Zerstörers (‘Destroyers’) attacked by day, his S-boats could attack by night
in a co-ordinated assault on British merchant shipping through the Channel.
Convoy OA178 had provided the perfect opportunity for Bütow to test
his theories. Despite the pasting the convoy had received that afternoon at
the hands of VIII Fliegerkorps, Bütow felt their effort had been somewhat
half-hearted. However, as four S-boats sped across the Channel, the chance
had come for the navy to show what they could do.
S-boat tactics were to cover the bulk of the distance in line astern, then,
as they neared the enemy targets, they would split into pairs, or Rotten, as
fighter aircraft also termed a pairing. The two pairs would then attack their
targets together, having first slowed to around ten knots. This was necessary
in order to fire the torpedoes; if they were going too fast, the speed would
affect the trajectory of the torpedo. The second advantage was that at lower
speeds the boats were considerably quieter.
It was around twenty minutes to midnight when the S-boats had a stroke
of luck. From the shore a searchlight was casting a beam out to sea, and