Hi Daniela, Dreams are so much fun to interpret. I am no expert, but this is what I found online:
"All vehicles appear to symbolize the way that we maneuver, or get through, a segment of our life's journey. A submarine is a powerful moving machine that travels through deep waters. Deep waters represent our emotions and our unconscious. A submarine could represent the way in which we are navigating through our emotional waters and deal with the materials that are coming up from our unconscious. A submarine can have negative or positive connotations. It could suggest that you are feeling strong and are prepared to aggressively deal with whatever issues and emotional concerns that arise in your life. On the other hand, the submarine as a dream symbol could be suggesting that you are overly guarded and defensive and are currently not open to airing of personal issues."