The loud noise that the soldiers make is compared to the loud noise of the sea. Alternate translation: "The sound that they make is very loud, like the sound of the sea" (See: [[rc://en/ta/man/jit/figs-simile]])
The phrase "set out in order" means that they have organized themselves and are riding in rows. The phrase "as men for battle" indicates that they are ready to fight. Alternate translation: "they are riding on horses in their assigned rows, and they are ready to fight"