The solo game offers five difficulty levels, and after choosing your level you're given the option of seeing a practice torpedo fired. You're only likely to choose this option once as the torpedo makes painfully slow progress through the water towards the enemy sub seen through your periscope. To be fair, this is the only part of the game which was slow, the rest responding pretty briskly to the keyboard or a Protek joystick.
There are three screens giving you the information you need; the Control Room and Chart Room down below, both with excellent graphics.
The first tasks to master to master are how to dive and surface successfully, which involves adjusting your ballast tanks and hydroplanes. You cannot stay underwater too long as the electric motors can only be recharged from the diesel engines on the surface. But stay on the surface too long and you risk the enemy submarine getting you first, or being spotted by a passing aircraft (this doesn't apply in the dual game).
You scroll from the Control Room to the Chart Room using the 'C' and 'X' keys, and these keyboard controls are sensibly laid out, using adjacent keys where possible, with a summary of the controls printed on the back of the instruction booklet.