Ships became associated with biscuits during the seventeenth to nineteenth centuries, when there was enough long-distance travel by ship for its ideas to become part of many cultures, but food preservation methods were quite limited, in the absence of refrigeration and modern packaging methods.
A "Ship's Biscuit" is a piece of hardtack, the mainstay of sailors' diets during the period. This is made from flour, salt and water, and baked much longer than modern-day biscuits. It keeps indefinitely if it can be kept dry and free from insects. It provides plenty of calories and a bit of protein, but no vitamin C, the absence of which made scurvy a common disease of sailors until James Cook demonstrated how to prevent it.
I've baked hardtack as an exercise in practical history. It does not taste bad, but it is amazingly hard, usually needing to be soaked in water, tea, or soup before eating. It's pretty dull if you have it as a large part of your diet, but grinding it will turn it back into salted flour, which you can cook with.