Understanding Hull Symbols

Ships and ship types are often talked about using a set of shorthand letters to designate types. DDG. CVN. LHA. SSBN. DLG. While there are some good guides to the system online, I figured I should explain them here as well.

These codes originate in a standard set by the USN in 1920, to overhaul the designations then in use. All ships were assigned a two-letter code, and numbered sequentially within the code for their type. Around the time of WWII, three-letter codes became necessary to designate the bewildering array of ship types developed for a global naval war. It's continued to evolve since that day, and many of the rules have changed at some point or another over the past century, but the bones of the system are still identifiable.

The most important information is the first letter or two. This will tell you the broad type at a glance, with later letters giving more information.

Certain letters hold very specific meanings, regardless of where they are in the code. The most important of these are G, N, and V. Within the USN, V is identified with all things having to do with fixed-wing aviation.⁵ So an AV would be an auxiliary for fixed-wing airplanes, which in practice was a seaplane tender. For combatant ships (first letters of B, C, D, F and S) N means that the ship is nuclear-powered, while G means that it carries guided missiles. In practice, all ships these days have at least some guided missiles for self-defense, and G is reserved for ships with either an area air-defense system, or lots and lots of cruise missiles. H is usually used for helicopters, but appears in designations more rarely. Lack of an H does not mean the ship doesn't have a helicopter.

Unfortunately, at this point the system starts to lose coherence. Almost all of the choices made in the system are logical, in the sense that the first letter of an appropriate word was used, but the same letter can be used for different things in different places. There are some fairly common ones (E for (ASW) escort, K for ASW hunter, R for radar pickets, M for mine warfare-related ships) but none of these are guaranteed to always work.

The situation is made even more complicated by the overhaul of the system done in 1975. Before that date, the USN had a classification of "frigate" with the hull symbol DL(G), which can be read as "destroyer leader" or "destroyer, large". These were ships that were bigger and better-armed than destroyers, but not up to the traditional standards of cruisers. The cruiser title was reserved for ships of the traditional cruiser size and type, which were coded as CLGs, all the heavy cruiser conversions having been retired. In most of the rest of the world, the frigates would have been called cruisers, while the term frigate was used for what the US called ocean escorts or destroyer escorts (code DE).

On June 30th, 1975, the US system was brought in line with that of the rest of the world. Most of the DLGs became CGs, while a few early ones became DDGs. The remaining CLGs became CGs, too. DE(G) was changed to FF(G), and the ships using that code became frigates.

Here's a chart of the major designations in surface combatants that aren't covered by the above table and the hard-and-fast rules. There are variations on these, but it should make it possible to understand a fairly typical ship list.

Submarine designation is, thankfully, relatively simple. The bare SS designation was common before the 1950s for diesel submarines, although SSK is more common for that purpose these days, to avoid confusion over whether SS is being used as a generic for all submarines or only for diesel attack boats. SSNs are nuclear attack submarines, while SSG(N)s carry cruise missiles and SSB(N)s carry ballistic missiles.

Auxiliaries and amphibious warfare vessels have their own set of rules, which are only loosely related to the combatant system. There is some cross-pollination, as a number of vessels have been transferred back and forth between the A and L designations. The following table has the more important codes for auxiliaries.

Note that in many cases, three-letter codes are built up from several two-letter codes, so an AOE is essentially an AO (oiler) plus an AE (ammunition ship) in a single vessel. Most of these types have several subvariants, which can be found on more comprehensive lists.

Amphibious warfare designations are rather interesting, as they are mostly later additions to the system. The majority take the form of LS for landing ship or LC for landing craft. The third letter determines the type. Other forms are found on a few ships.

This system is only used officially by the USN, but it is also used in slight variations by reference books and naval geeks worldwide. This post should have given enough of a background to be able to use that version, and if you want the full list, including never-used, massively obsolete, and very specialized designations, check out the comprehensive list on NavWeps.