My old Battalion 78-82 Civic Action Team 7415
The battalion itself (main body) 'mounts out' by sea? I don't think so.
Not in modern times. They travel by military aircraft or by chartered airline.
Yes, the Seabees used to travel with their equipment and materiel by sea for deployments. Air travel for the entire unit was a luxury not standard for personnel until the early 1960s.
That was my Battalion as well, I was in Rota from 80 to 81, Charlie company, I was on the marginal wharf project with Paul Lawrence