Does anyone know how to solve the hidden teleportation ring quest?

[U-95]

Dive and locate the sea dragon, whose lair is somewhere in the sea, with your hydrophones and torpedo it before it finds you and melt your submarine with its corrosive alcaline breath. Surely, you'll not kill it so, so surface and finish it with the deck gun.
When it seems to be dead, close carefully and look for the ring in the dragon's belly, where it's incrustated. Get it before the dragon's corpse disappears forever below the waters; otherwise, you'll have to travel at *1/2 speed time to the Caribbean sea, where legends say there's another teleportation ring.

[weeksatsea]

Originally Posted by U-95

Dive and locate the sea dragon, ......

..but remember that you need to find the golden ladder and go down it before you can dive.

[derblaueClaus]

Originally Posted by U-95

Dive and locate the sea dragon, whose lair is somewhere in the sea, with your hydrophones and torpedo it before it finds you and melt your submarine with its corrosive alcaline breath.

Well thats not the whole truth. If you ended the Quest "Hunt for the golden Hood" successfull you will be awarded an anti-corrosive paint Mk2 by the Führer himself, wich will protect you against the Dragons breath. So you can also ram him to death with this.