From the colonization of the New World in days of old on Earth to the colonization of the stars, the transportation of food, weapons, medical supplies, or people, whether they be civilian or military, has always been a concern to both kings and generals.  Space transport ships come in all shapes and sizes.  From the huge bulk container ships with 100 crew, to the tiny 2-3 man tramp frieghters.  Be it for profit or pressed into service, these ships keep supplies lines between the stars or military actions moving along.  They also double as targets of opportunity for would be pirates or enemy launched attacks.