Why Are Submarines Called Boats? The History Behind The Term

Modern nuclear submarines are some of the most complex machines of war ever constructed. They can remain at sea for years, can submerge for extended lengths of time, and they run almost silently. They are considerably more advanced than the diesel-powered subs of the mid-20th century, and even those were impressive pieces of military hardware. If you happen to see a submarine docked somewhere and compliment the vessel to a nearby submariner, there's one thing you shouldn't do: call it a ship.

Despite their size, complexity, and uses in and out of combat, submarines are referred to as boats, not ships. While this makes sense to submariners and other sailors working on surface ships, it's not something average people know or understand. The line between what is and isn't a ship isn't known to all, and the words are often interchangeable. That's true of a variety of watercraft, but it isn't for submarines, which have always been called boats.

The reason for this extends throughout the history of submarines, which goes back quite a bit further than people realize. Some of the earliest submarines sailed long before the 1900s, and it took centuries for the technology to get to the place it is now. Understanding the history of subs shines a light on why they're called boats because it's to do with their initial size, means of transport, and more than anything, naval tradition. Still, it's important to understand what is typically classified these days as a boat and what's classified as a ship, even if the terms are a bit loosely applied.

There are many schools of thought regarding the terms ship and boat, so to keep things simple, a great source is the U.S. Navy Institute. Lt. Cmdr. Thomas J. Cutler, U.S. Navy (Retired) explains that "One of the quickest ways to establish yourself as a naval novice is to refer to a ship as a boat." The opposite is certainly true as well, but it breaks down as follows: a boat is a watercraft that is small enough to be carried on a larger vessel, which is called a ship.

Essentially, this can be expressed as "A ship can carry a boat, but a boat can never carry a ship." In the Navy, if a vessel, regardless of its size, has a permanent crew and commanding officer assigned, it's most often referred to as a ship. Conversely, if the vessel is only manned when it's being used, it's likely a boat. Of course, these are more guidelines than rules, and various watercraft throughout history have struggled with a bit of an identity crisis regarding this type of designation.

During the Vietnam War, special vessels called Patrol Craft Fast (PCF) were constructed for use in rivers. These small craft sported a permanent crew and commanding officer but were most often referred to as "Swift Boats," so there are no set guidelines that establish the classification of a boat or a ship so much as tradition. That's certainly why we call the many modern submarines in the U.S. Navy boats instead of ships, and the history goes back a long time.

Given the guidelines mentioned above, anyone looking at a modern submarine is going to call it a ship. After all, they're massive vessels, some of which carry smaller watercraft, so they look and act like ships. Tradition says otherwise, and it goes back to the dawn of submarine technology. Initially, submarines were much smaller than they are today. They were typically built out of wood and were sealed with some sort of resin. These vessels could keep a single occupant or small crew submerged, using hoses to bring in air.

Early subs were also transported via larger vessels, and because of these factors, they were always referred to as boats. As technology improved and submarines became more robust fighting vessels, they should have been reclassified as ships — it only makes sense given their size, uses in combat, and more. Still, tradition often wins out, especially in the world's navies, and as a result, we still refer to submarines as boats long after they should have been called ships.

Granted, there are different types of subs that could be called boats based on normal terminology. The United States' only midget submarine, the SS X-1, could be called a boat were it not already. Regardless, it doesn't matter because the Navy is unlikely to change this practice. Tradition is incredibly important to the identity of the U.S. Navy, as well as other navies around the world, and if there's one thing that's going to keep people calling submarines "boats," it's naval tradition.