Introduction to the five young officers who are taking part in the Perisher Course as they begin the all-important sea phase of the course. It’s straight in at the deep end as the face one of the toughest training exercises ever devised, called “Eyes Only”. Basically, using only a periscope and a stop watch they must play “chicken” with charging warships. The object is to dive if and when a warship gets dangerously close. There’s a very real danger of calamitous collision and Teacher must take over more than once to swiftly dive the submarine out of danger The students also face the seemingly straightforward task of loading and unloading specialist reconnaissance troops, dropped by helicopter into a remote Scottish sea loch. The dress rehearsal turns to farce and the students must get their act together fast or face the chop.