I suspect I was lucky.
The Salta I set to creep at periscope depth and it found what was likely to be the invasion force almost immediately. Once the force got closer I went above the layer and waited. The Salta identified the frigate and the 'Olwen' so I manually targeted, what I assumed to be, the two transports, one of which sank immediately, the Olwen remaining afloat despite a substantial 'hit'. I also managed to get off a torpedo at the frigate before the Salta started (automatically) avoiding the incoming torpedoes, presumably from the British sub which I never located. I put one helicopter in the air with a view to finishing off the Olwen but that sunk just as the chopper arrived and as one of the frigates had been hit by the torpedo fired earlier the helicopter finished that off without encountering any return fire.
The Salta having successfully avoided the 3-4 incoming torpedoes had in the interim fired two torpedoes manually at the Phoebe and the scenario (automatically) ended with the Phoebe departing stage left hotly pursued by two torpedoes. And with two, presumably, homeless, helicopters angrily buzzing around the Salta which, by then, was sitting happily on the bottom.
Although the two ships were heading towards the battle zone neither they nor the remaining helicopters played a part in the fight
So I got 200 points and a Triumph (which makes a change from the normal 'minus' figure I usually achieve.....)
An excellent scenario with, I suspect, considerable replay value.
Many thanks, Meroka37.