The ship types of World War II

The origins of WWII vessels

The month of October is closely tied to the birth of the U.S. Navy. The Continental Navy was formed on October 13, 1775. Navy Day was celebrated on October 27 from 1922 till 1949, when it was replaced by Armed Forces Day. This article pays homage to the U.S. Navy and its history by explaining the origins of some of the warship types that were used in World War II.
 
Battleships. Battleships were the biggest, toughest gun-armed vessels, whose primary job was to engage and destroy other ships. Contrarily to what you might think, however, they’re not called “battleships” simply because they were meant to fight battles – all warships do that, after all.
Ship design during the Age of Sail faced two fundamental limitations. Firstly, seagoing ships were propelled by sails and could not sail into the wind. Secondly, most of their cannons were placed on gun decks and pointed sideways, since that’s where there was enough space for them. This meant that the primary means of attack would be devastating broadsides aimed port or starboard. And with broadsides, the thing a captain wanted the least in a battle was to receive raking fire.

The above image is an example of raking fire. The yellow ship has her side (and half of her guns) presented toward the red ship, while the red ship can only return fire with the few guns pointed ahead. Additionally, the cannonballs that hit the red ship will hit the structurally weak bow (in this case) or stern (if the yellow ship approached from the other side), then travel down the length of the vessel, wreaking much havoc. The few shots that hit the yellow ship travel across its breadth, causing far less damage.
 
Naval powers invented a tactic to prevent their ships from taking raking fire: the line of battle. The ships of a fleet would line up, one behind the other, and move in a line. In this formation, the enemy’s vessels couldn’t maneuver in front of or behind yours, since you already had your other ships in those positions. This offered the best overall protection for your fleet. (It should be noted that line-of-battle tactics were actually much more complex than that, with lines approaching each other at various angles and intersecting each other, admirals dividing their forces into multiple lines, and the lines themselves maneuvering, but such details are beyond the scope of this article.) The line of battle survived the Age of Sail, and in fact only fell out of use during World War II, when fleet carriers and naval aviation finally rendered gun-armed capital ships obsolete.

The line of battle offered good enough protection against raking fire, but it had its own weakness. Once your line was formed, you couldn’t swap the ships around; they were locked into the formation. This became a problem if one of the smaller, weaker ships in your line ended up exchanging fire with a much bigger, heavier-armed ship in the enemy’s line, since your vessel didn’t stand a chance. The solution was to only put your biggest, heaviest ships in your line of battle, the ones that stood a chance against the enemy’s heaviest ships. Smaller ships would be kept out of the line and relegated to skirmishing with the enemy’s smaller ships. The big, heavy, well-armed vessels suitable to fight in the line became collectively known as “ships of the line of battle,” which was eventually contracted to “ship of the line,” or alternatively as “line of battle ships,” which was shortened to “battle ship,” then later “battleship.”

Ship design underwent revolutionary changes in the late 19th and early 20th centuries. Sails were abandoned in favor of steam engines and later diesels (for smaller vessels at first), freeing ships to maneuver with no regard to the wind. The numerous cannons used in broadsides were replaced by a smaller number of heavier guns mounted in rotating turrets that allowed ships to engage enemies from any angle. The name “battleship,” however, stuck around to describe the largest, most heavily armed and best-armored ships.

Cruisers. The word “cruiser” originally meant not a specific type of ship, but rather a type of mission that many different ships could undertake. The word ultimately comes from Latin crux, “cross.” The Dutch started to use the word kruisen in the mid-17th century to describe a ship crossing large distances on open waters, “cruising,” such as when crossing the Atlantic. A navy didn’t want to use their ships of the line for such missions: they were heavy and slow, too expensive to risk losing somewhere on the far side of the world, and too strategically important to send far away from home for a long time. Instead, they wanted something smaller, lighter and faster, but still heavily armed and sturdy enough to survive open waters and defend itself. Frigates, which we’ll talk more about later, and smaller sloops were typical “cruiser” ships.

The advent of steam power and first ironclad then later steel hulls turned the cruiser into a specific ship type – or rather, many specific types in the late 19th and early 20th century. Protected and armored cruisers were the first to have additional armor plating in vital locations, the difference being which parts were armored. Armor eventually became a standard feature on warships, and new distinctions appeared. Light and heavy cruisers differed not so much in weight, but in the caliber of their guns. Auxiliary cruisers were used to raid enemy merchant shipping, and scout cruisers were, appropriately, dedicated to scouting ahead of a fleet. In general, however, cruisers stayed true to their origins by being fast, long-ranged vessels able to defeat similar-sized or smaller targets with their guns.

After World War I, the Washington Naval Treaty of 1922 and the London Naval Treaty of 1930 aimed to prevent a cripplingly expensive proliferation of warships. To this end, the treaties declared limits on how many and how heavy ships the signatory nations (the United States, the United Kingdom, Japan, France and Italy) were allowed to build. These treaties necessarily codified various ship types by displacement and armament, with different limits for different types. Light and heavy cruisers could both have a maximum displacement of 10,000 tons, but light cruisers were limited to guns of up to 6.1 inch (155 mm), while heavy ones could have guns of up to 8 inches (203 mm). Anything over 10,000 tons of displacement was classified as a capital ship with much stricter limits on numbers.

These limitations, as well as general considerations of ship design even before World War I, forced ship designers to try and get the biggest bang for their buck. Many details factor into designing a good warship, but one fundamental issue is the balance of firepower, armor and speed. You want more firepower? You can use bigger or more guns, but they make the ship heavy, and thus slower. More survivability? You need thicker armor or more surfaces covered by it, but again, it makes you heavy and slow. You want a faster ship? You need to lighten the vessel and have fewer, smaller guns or less armor. (Or design a much larger ship with enough space for massive engines, but that’s prohibitively expensive, and also violates cruiser displacement restrictions after the Washington Naval Treaty.)
 
One notable idea that came up during this balancing act was to emphasize firepower and speed, sacrificing armor. Even before World War I, the battlecruiser followed this concept. It was a ship somewhere between a cruiser and a battleship, with the speed of the former and the firepower of the latter. Such a ship was, in theory, fast enough to flee from battleships and to chase down anything else, and had enough armament to make short work of normal cruisers and anything smaller.

Battlecruisers were built for and after World War I, and the surviving ones were growing obsolete by World War II. The Royal Navy and the Imperial Japanese Navy rebuilt their battlecruisers to more modern specification to keep them relevant. The notable exception was HMS Hood, which was famously and very rapidly sunk by the German battleship Bismarck in 1941. Even the updated ships fared poorly in the end due to their fundamentally weak armor, with only a single battlecruiser surviving the war.

The idea of a fast, heavily armed ship still persisted, with such more modern designs as the American Alaska class “large cruiser” introduced in 1944, or the “fast battleships” of the war, such as the North Carolina, South Carolina, Iowa, the British King George V, the German Bismarck and the Japanese Yamato classes. All of these followed the same basic scheme of high speed at the expense of some firepower or armor, only built to a larger scale.

Destroyers. One major naval innovation in the second half of the 19th century was the torpedo, a weapon that allowed a smaller ship to punch well above its weight. This weapon quickly led to the adoption of torpedo boats: small, cheap vessels that could swarm a battleship or cruiser and destroy it. Due to their small size, these ships had a short range and poor seakeeping, which restricted their use to coastal areas; the ideal use for such a flotilla would be to break the blockade of a port by capital ships. The Patrol Torpedo boats (Read our earlier article – The “devil boats” of America) and other similar vessels of World War II, such as the German E-boot, were descendants of the torpedo boat concept.

Naval planners saw these new vessels as highly dangerous, and were quick to develop a counter. The unimaginatively named torpedo boat destroyer’s job was to destroy torpedo boats. The first such ships settled the fundamental design: they were larger than torpedo boats (some by a little, others by a lot), were hopefully fast enough to intercept the boats, and were primarily armed with quick-firing low-caliber guns that could make short work of the attackers. It was quickly recognized that you could also just put torpedoes on your torpedo boat destroyers, since they could do the job well enough, and then you wouldn’t need dedicated torpedo boats. Another change was to the name: it was shortened to the more manageable “destroyer” – at least in English; several languages still use names that reflect the ship type’s original purpose of hunting or destroying torpedo boats.

The destroyer was recognized as a relatively small (and therefore relatively cheap) multifunctional ship by World War I, and war planners started giving it even more functions. Beside catching enemy destroyers and attacking the enemy’s larger ships with their own torpedoes, they were also used to screen fleets, search coasts for enemy presence, and watch enemy ports.
 
World War I was notable for the introduction of submarines, and destroyers were given the job of guarding fleets of capital ships and cruisers against submarine attacks. Their high speed allowed them to intercept the submarines and ram them if necessary, and their quick-firing guns could destroy a surfaced sub. Their shallow draft meant that torpedoes launched against them would likely pass underneath the ship. Destroyers were also equipped with hydrophones to locate enemy subs, and depth charges, which were specifically developed against underwater targets. When Imperial Germany commenced unrestricted submarine warfare in 1917 and started going after unarmed convoys with U-boats, destroyers were quickly detailed to escort these slow and vulnerable targets.

Escorting fleets and convoys remained one of a destroyer’s mainstay tasks in World War II, but technological advancement presented yet another challenge. Destroyers had to be fast, with a speed of around 25-35 knots (29-40 mph), to keep up with capital ships and cruisers. Convoys in the Atlantic and elsewhere, however, were comprised of sluggish transport ships, and assigning 36-knot-fast destroyers to a convoy that would only steam at 10-12 knots (11-14 mph) was a waste of resources. Additionally, while destroyers were relatively cheap compared to cruisers, battleships or carriers, they were nevertheless expensive vessels, and providing naval fleets and convoys with enough escorts was a major financial drain. Therefore, a new ship type was devised, the destroyer escort.

The destroyer escort was essentially a small, slow, cheap destroyer with a speed of around 20 knots (23 mph) and an armament specialized against submarines, while proper destroyers, sometimes called “fleet destroyers,” had a more well-rounded weapon selection that allowed them to also engage aircraft and smaller surface vessels. Destroyer escorts also had a tighter turn radius which allowed them to better evade torpedoes and maneuver to attack. The slow speed was a fair tradeoff, since the convoys would not be travelling that fast, and the destroyers’ sonars wouldn’t work properly at speeds over 20 knots, anyway.
 
Frigate was the Royal Navy’s term for some classes of destroyer escorts, and like “battleship” and “cruiser,” the term harkened back to the Age of Sail. The word “frigate” was originally used to describe lighter, oared galley-type ships use in the Mediterranean in the late 15th century. The origins of the name are uncertain, but it might come from Ancient Greek “aphraktos naus,” “undefended ship.” (It should also be noted that frigatebirds, a family of seabirds, were named after the ship type, not the other way around.) The name was applied to a new type of ship in the 16th and early 17th century, a maneuverable sailing ships used by Spanish privateers against Dutch shipping. The Dutch, in turn, adopted the name for their own long-hulled ships that combined speed, a shallow draft to maneuver in the coastal waters of the Netherlands, and sufficiently heavy armament to deter privateers and stand up to Spanish warships.

By the mid-18th century, the frigate was understood to be a fast warship which was distinguished from ships of the line by only having a single gun deck rather than several. Many frigates were used in the cruiser role and undertook long independent voyages.
 
The advent of turrets rendered the frigate’s distinction moot: the idea that a ship only has one gun deck became meaningless in an era when ships no longer had any gun decks at all. “Frigate” fell out of naval terminology until the British resurrected the word in World War II and applied it to some of their escort destroyers. This new use established the notion that a frigate is a smaller warship than a destroyer, though this distinction became rather blurry in modern times.

One big category of ships we have not talked about are the carriers designed to transport and operate warplanes. The earliest carriers were some seaplane tenders, which appeared shortly before World War I. A tender serviced seaplanes and flying boats, and the larger ones could also carry some onboard. Seaplane carriers were tenders large enough to only to carry planes onboard but to also house repair facilities. The planes were placed on the water with cranes for takeoff, then lifted back up after landing. This was a slow process, and the seaplane tender quickly grew obsolete. It still saw some use in World War II: both the U.S. and the Japanese Navy had built a number of them. These ships were not used on the open seas. Instead, they operated at newly constructed bases which did not yet have runways built. Germany also operated a number of seaplane tenders, but, interestingly, these were used not by the Kriegsmarine, the navy, but the Luftwaffe, the air force.

Experiments with flat-deck carriers, which wheeled aircraft could take off from and land on, also began before World War I. The Japanese Hōshō became the first purpose-built carrier (rather than a converted ship) in 1922.
 
Carriers diversified during World War II. Escort carriers were small, slow vessels carrying 20-30 aircraft. As their name suggests, they were originally used to escort oceanic convoys and protect them from U-boats with their anti-submarine planes. Later in the war, escort carriers were also placed into hunter-killer groups that proactively sought out enemy subs. These small carriers, however, didn’t have the aircraft to stand up against gun-armed capital ships, as demonstrated by the Battle off Samar (Read our earlier article – “Survival cannot be expected”).

Merchant aircraft carriers were a stopgap British solution to the same problem of vulnerable convoys. These were converted merchant ships with a flat top, carrying six planes and also some cargo.
 
Meanwhile, fleet carriers went the other way: they were large, capable of carrying 50-90 aircraft, and fast enough to keep up with other capital ships as part of a fleet. During the course of World War II, fleet carriers have proven their supremacy over battleships in large-scale naval engagements. The line-of-battle tactic that originally gave birth to the battleship fell out of use for good, and was replaced by the carrier fleet, with the carriers at the center and all other ships surrounding them in concentric circles for protection.

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Veterans Day originates from Armistice Day marking the end of World War I, which formally ended on November 11, 1918. It is still known as Armistice Day in France and Belgium, while the UK and Commonwealth countries celebrate Remembrance Day or Poppy Day.