[Capt. Morgan]

The convoy attack scenario takes place before the war starts, so those escorts are neutral - you can run circles around the them and they won't attack you (until you initiate an attack).

In war time you would find it very difficult to get that close to a R.N. destroyer on the surface. At longer range, a destroyers gunfire will be much more accurate than your subs, and Also, a destroyer can bring between four to six guns to bare whereas you only have one. Hence the reluctance you see here to attack destroyers on the surface in wartime.