Hazrat Ka'b al-Ahbar (may Allah have mercy on him) says: "The warrior of the sea has superiority over the warrior of the land, because when he sets foot in the sea, the gates of Paradise are opened. If he is killed or drowned, he receives the reward of two martyrs."
Hadith Referenceسنن سعید بن منصور / كتاب الجهاد / 3575