A year before "The Deep" (perhaps the first known underwater shooter), the Tecfri guys released a game that technically was ahead of his time, but once again it was completely ruined by the non-existent difficulty curve.

If already in itself, is a little claustrophobic the underwater environment, imagine if in addition you have to avoid the bullets of the enemy, we must overcome the remnants of these enemies, without hitting any rock or ledge...
Sauron is so difficult than the people of "MAME Team" thinks it's a bug (a bug that we know well, called "Spanish game").

Technically, the game is flawless, with smooth scroll, graphics ahead of its time and is very varied, the sound is not bad either, and even has scans of voice. We have many types of weapons to choose from, there are final enemies, and even it has a stage where the action moves to the air, converting the submarine on a plane (which softens rather the difficulty).