From the back of the box:
The free world is in peril - war has been declared and the enemy is closing in. Your weakest point is the coastline so a strategic defence initiative has been adopted.
Your mission - is to patrol and defend the inner sea using all the modern weapons systems with which you have been supplied.
Seawolf - a deadly accurate missile for use against both aeroplane and anti-ship missiles.
Exocet - a video linked rocket for attack upon surface ships.
Anti Submarine Helicopter - attach the enemy submarines using your depth charges.
The future of the country lies in your hands; frighteningly powerful weapons are at your disposal and important decisions must be made.
Convoy Raider is a simulation of a modern (presumably British, given the weapon loadout) naval vessel tasked with patrolling the local waters with an aim of finding and sinking enemy ships and submarines. Of course the ships and submarines shoot back, and are augmented with aircraft which also threaten your ship.
The player can understand the immediate tactical situation using a Radar screen. This is in two parts, with the top showing surface and aerial threats, and the bottom showing submarines. More widely, the Map view allows your ship to be moved and also shows enemies.
You are armed with two types of guided missiles - the Seawolf for aeroplanes and incoming missiles, and the Exocet for attacking enemy shipping. Missiles must be remotely steered to their targets, then as they get close, the correct target on the horizon must be selected.
The helicopter can be used to attack submarines with depth charges, however the submarine can retaliate with surface-to-air missiles.
Damage is shown on a silhouette of your ship and can be repaired by rendezvousing with a repair ship. The manual helpfully states "Colliding with land causes extensive damage".