My brother,nephew,cousins, 20 of my male high school classmates work in ships(cargo,oil tanker,cruise ect.) all hold a bachelor degree of either marine transportation or marine engineering.As I remember they talk about they really never allow any kind of guns on board. I think ships owner simply don't want any liability in case crew member shooting each other or shooting the wrong guy. Even if they hire civilian security guard they still not protected with the Rules of Engagement that our military is overseas. It's illegal to carry weapon in international water unless you are purely military. My brother use to tell me that they haul farm machinery from U.S and bring them in Europe and coming back they haul cars from Europe to U.S . My nephew ship haul grains (corn,soybeans,milo,oats,wheat) from Louisiana and take them  either in japan or middle east.