In my scenario the raider approached the convoy from astern, appearing as a straggler. The attack was launched as a complete surprise at almost point blank range, using wolf pack tactics of attacking inside the convoy. In the resulting panic and confusion there is no order to scatter, ships are blinded as to their adversary and so end up shooting at each other, and as they try to avoid enemy fire there are collisions. This collateral damage aids the raider: in one hour say twelve ships go down at your quoted rate of one every five minutes, including losses due from tanker and ammuntion ship explosions, in each of the following two hours four more ships go down, which is how I arrived at my tally of twenty in three hours.
You say dream on. Well, it could have happened......couldn't it?
I dont think so , in the chaos and confusion of a night action , which is happening in roughish weather , remember , I think you are looking at a lower tally .
If you take a convoy interception which does mimic this , several warships getting into a dozing convoy at night , we can look at the Royal Naval Light cruiser squadron attacking the German troop convoy north of Crete in May 1941 during the Battle of Crete .
Mostly the targets were Caiques , a big wooden trawler/cargo coaster type common in the Levant , with some few small passenger ferry steamers , escorted by Italian Torpedo boats ( small destroyers ) .
In good fair clear weather the cruisers achieved complete surprise , lighting up the targets with searchlights as well as by star-shells , and were close enough to engage with pom-poms and the quad 0.50 mg mounts , as well as main/secondary armament , but , far from being the complete destruction one would expect from a sustained attack ,( this wasn't just a quick charge through ) two thirds of the vessels attacked survived , and although this seaborne thrust at Crete was turned back and scattered , and the troop units thoroughly disheartened , they were far from annihilated .
The thing was that the British command and control soon broke down due to all the chaos of flashing lights and guns going off and gunsmoke and smoke from fires ( and I think their Italian escorts also tried to lay some smoke screening ) .
It would be like being in the noisiest of Discos with the fog machines on overdrive , every light in action and a severe riot taking place at the same time .
The Gunnery teams at the directors couldn't see to designate the targets and so it was the guys at the gunmounts who either waited for the word , or couldn't see either , or who let fly at something already dealt with .
I suppose the only Naval lesson to draw would be that close melee action was no longer a thing which the major units of the fleet were efficient at , something which to a degree the earlier battles of Narvik had also shown .
" Relax ! No-one else is going to be fool enough to be sailing about in this fog ."