In the first screen you face one enemy submarine and three planes overhead that keep dropping bombs, but they fall too slowly to make this scene much of a challenge. Enemy subs do nothing but get in the way and are easily sunk from beneath -- and make sure you do that before shooting the last of the planes. When that happens, a dive bomber appears and you need all the maneuvering room you can find. You don't want to worry about the enemy sub now, because the dive bomber doesn't fly in as a predictable pattern as the other planes, and its bombs are heat seekers. This was my favorite scene, and it proved quite challenging to learn a technique for dealing with this small enemy. Somehow you must let the bomb get on your level, dodge it, then surface for a quick shot at the bomber before it turns and dives again.
As soon as you hit the dive bomber, the navigation screen appears. It's sort of like playing River Raid without many enemies -- you just have to stay in the blue water. The channel maze you must navigate is easily learned, however, and becomes tedious after several plays, especially the first navigation screen. It's only for practice and contains no enemy mines to shoot. The mines, which you find in all succeeding channels, are just X shapes that dance back and forth. When you hit one, the whole line of three disappears. The submarine makes a nice sonar-ping noise throughout this scene, but it is only used for effect when it could have been part of the gameplay. Think about it: As the maze scrolls your way you could navigate by sonar. No noise would mean a clear passage. Games could really be awesome.
Everyone starts off on the same foot in this game, or at the same skill level anyway, because there is only one. This can be frustrating for the better player who would rather enter the game "in progress." In short, Polaris is challenging, particularly as the speed and number of enemies increase, but in this case the whole is less than the sum of its parts.