Classifying Modern Warships - Part I (Background)

The numerous rigs that defined ship type in the age of sail

Today there is some confusion about how modern warships should be described. Terms such as "destroyer," "frigate," and "corvette" are commonly thrown around, but it is impossible to find any agreed upon definition as to what they actually mean. It becomes even more complicated when attempting to compare warships from multiple nations, such as the Franco-Italian Horizon-class - which are known as "frigates" (frégate) by the French and "destroyers" (cacciatorpediniere) by the Italians, and are the product of the "Common Next Generation Frigate" program but have NATO "D" for destroyer hull numbers. However, before attempting to lay out a rational system for comparing modern warships, let us first briefly examine the history behind warship classifications.

Beginning in ancient days with the development of dedicated warships, classification was largely based on the method of propulsion. The Greeks, for instance, classified their warships based on how many banks of oars the vessels carried, giving us descriptions such as "bireme" and "trireme." Even as sails increasingly replaced oars in the later Medieval period, the focus on propulsion remained. First with classifications such as "galleon," "galleass," and "galley" based on the extent to which the ship used sails and oars. And then, as oars disappeared, with classifications describing the sailing rig of the ship.

But while sailing terms such as "brig," "cutter," and "sloop" continued to define smaller warships types well into 19th century, the 17th century saw the rise of a new system of classification based on firepower. Until then, naval warfare had continued to be defined by the same tactics of ramming and boarding pioneered in the ancient world. However, the introduction of cannon swiftly revolutionized naval tactics and the most important feature of a warship became how much firepower it carried. Thus, the famous system of "rating" ships based on the number of guns they carried came into being.

This system provided an excellent means of classifying warships until the mid-19th century, when ship design took several drastic changes. First, propulsion again took center stage with the introduction of the steam engine. Second, larger guns and explosive shells meant that sheer number of guns was no longer as meaningful as it had been before. And third, the introduction of armor plate meant the durability largely superseded firepower as the defining characteristic of a warship. This led to new, somewhat haphazard, classification system that focused on propulsion and armor, with terms such as "ironclad" and "steam-frigate."

As the transitional period ended and steam propulsion became universal, a new classification system based purely on armor was introduced. The most heavily armored ships were now termed "battleships," while more lightly armored ships were classified as "cruisers," which were in turn subdivided into "armored cruisers," "protected cruisers," and "peace cruisers" based on their amount of armor (or lack thereof). This armor-based system indirectly led to a partial reintroduction of a firepower-based system, as ships with heavier armor also carried more powerful guns to punch through the similar armor of their counterparts. However, armor remained the most important characteristic, as demonstrated by the lightly armored "battlecruisers" being seen as cruisers despite their battleship-caliber guns.

But this stability did not last long and new technologies of the 20th century turned naval warfare on its head. The self-propelled torpedo, the submarine, and airplane meant that naval warfare was no longer a matter of the larger ship trumping the smaller. Instead, it became more of a rock-paper-scissors contest where different types of vessel each had their own strengths and weaknesses, and a fleet needed to make use of combined arms to prevail. This led to the ships being classified based on their tactical purpose instead of their technical characteristics. "Torpedo boat," "destroyer," "destroyer leader," "scout cruiser," "seaplane tender," "aircraft carrier," "submarine," etc. Although these terms conjure images of specific ship configurations, at their heart they are really descriptions of roles rather than of physical attributes.

The artificial ship types of the treaty era - note how the "heavy" and "light" cruisers are nearly identical in size and purpose and were virtually interchangeable in wartime

However, this revolutionary shift in ship classification has been largely masked by the postwar naval treaties. Beginning with the Washington Treaty of 1922, these agreements were the first international legal definitions of warship types. And being political documents, they completely missed the reality of warship design in favor of classifying warships by the easily-measured attributes of displacement and gun size. These artificial types grouped wildly different ships, such as battleships and battlecruisers or armored cruisers and scout cruisers. And because navies sought the every advantage they could squeeze out of the treaties, they largely built to the treaty maximums rather than to properly fill necessary tactical roles.

This effectively killed off several fairly important warship types and ended purpose-driven warship design. However, the artificiality of these treaty types can be seen in the veritable explosion of new ship types following the demise of the treaty regime in the late 1930's. From the Deutschland and Alaska "cruiser-killers," to the Atlanta and Dido "AA cruisers," to the plethora of ASW escorts, a new wave of purpose-driven warship types were created to fill gaps in the combined arms team left by the obsolete thinking behind the treaty classifications. Somewhat confusingly however, obsolete terminology such as "frigate" and "sloop" was resurrected to describe many of these new ship types. The design of purpose-driven warships continued into the postwar era, with new technologies leading to the development of even more tactical roles such as "radar pickets," "guided missile cruisers," and "hunter-killer submarines." The introduction of nuclear power also meant that some ships were again classified based on their method of propulsion.

But as technology and tactical thought matured in the second half the 20th century, the bewildering number of purpose-driven ship types began dwindling as navies increasingly designed multi-role replacements. Today it is rare to find a surface combatant that is not capable of some level of air defense, antisubmarine warfare, antiship warfare, and land attack, or to find a submarine that is not equally capable of hunting submarines, sinking surface ships, and firing cruise missiles. However, on a larger scale naval warfare continues to be dominated by heterogeneous combined-arms fleets - aircraft carriers, surface combatants, and submarines each have their own distinct role to play even if each of those categories is more homogenous than before.

To be continued…