Developed in the late 19th century to combat torpedo boats (hence their original name "torpedo-boat destroyer"), they gradually took over the role of the torpedo boats themselves, but lacked speed and operating range. Over time, improvements in engine design allowed them to overcome this deficiency, and naval commanders began to utilize them more often than any other type of ship due to their new-found flexibility, lower operational costs, and ease of quick deployment. Destroyer development post-World War I was heavily influenced by the very successful V and W classes of the Royal Navy, although the various nations would eventually branch out into very different design philosophies brought about by the unique circumstances they found themselves in. The Imperial Japanese Navy in particular placed great emphasis on the development of destroyers and torpedoes, being acutely aware of Japan's numerical and industrial inferiority compared to western nations. After World War II, with the advent of long-range anti-surface and anti-air missile technology, along with the widespread use of helicopters, destroyers evolved to be the workhorse ship of modern navies throughout the world.
While all destroyers have excellent speed, maneuverability and concealment, their most dreaded weapon is the torpedo; their effective use is directly correlated with the effectiveness of the destroyer (each nation has their differences, however). Torpedoes can cripple or outright destroy any type and class of ship they encounter as long as they can hit them, and they do not reveal the destroyer's location when launched, making them excellent assassins. Well-placed torpedo salvoes are an art form, be it having torpedoes "appear" out of nowhere, fired pre-emptively around land masses or used as area denial in narrow straits. However, unlike shells fired from guns, torpedoes have longer travel times, do not have the benefit of arcing over land masses, and as mentioned earlier, do not differentiate between friend or foe; destroyer captains should always be aware of nearby teammates such that the latter does not end up being sunk instead of the enemy.
In addition, the locations of torpedo tubes falls into two main configurations: one can launch torpedoes off both sides of the ship on 360-degree swivel mounts and the other can only launch them off either sides of the ship. Both have their advantages and disadvantages: ships using 360-degree mounts have large firing arcs, can easily bring their entire torpedo arsenal to bear on a single target and escape afterwards in a "shoot-and-scoot" tactic, especially useful for destroyers, but these tubes are often exposed on the top decks and vulnerable to damage from enemy fire; tubes located along the sides of the ships are usually protected but have limited firing arcs (although this also means that the tubes spend less time turning to aim at the target as well) and the ship has to expose both sides to fully utilize her torpedoes.
While their purpose is nearly universal, they vary based on nationality. Japanese destroyers severely lack gun firepower compared to their contemporaries, are extremely fragile, and are can do little else but attempt to flee if spotted by hostile ships; in exchange, they all can torpedo their targets beyond detection range and have the strongest torpedoes in their respective tiers. The United States has "brawling" destroyers that have the fastest guns and a good balance of torpedoes that lack range, but nonetheless are still lethal. However, their shells take a significant amount of time to reach their target, making them ill-suited to shoot fast-moving targets at range. In addition, they are able to begin equipping the Defensive AA Fire at Tier V — normally exclusive to cruisers — making them surprisingly effective against enemy aircraft. Russian and Soviet destroyers are almost light cruisers in that their primary armament is their guns — not their torpedoes, which are woefully underpowered for their respective tiers — and they lack concealment. Instead, they make up for that with incredible speeds that make them nearly impossible to hit and massive health pools that surpass other nations by far; their main battery guns are nothing to be taken lightly. Finally, German destroyers frequently find themselves in a middle ground between their Soviet and American counterparts, with above average stealth, good gun ballistics, and long-range torpedoes; however, slower turret traverse and rudder shift times combine with large turning circles mean they are not as difficult to hit when spotted and make them less attractive for the close-range "brawling" that the American line excels at. Their smoke screens are also the shortest lasting of any ships. They do, however, have an ace in the hole in that they gain access to the Hydroacoustic Search consumable through the latter half of the tech tree, turning them into dangerous hunters of enemies lurking in smoke.Destroyers also have 2 main consumables: Smoke Generator and Engine Boost. Smoke Generator lays down vision-obscuring smoke every few seconds, hiding the destroyer (and anything behind it) as long as the destroyer stays within the smoke for long enough to lay the next puff of smoke, or keeping the smoke screen between them and the enemy. Smoke screens however, also work both ways; they can hide the enemy if you let them go behind or into it as well. They also do not obscure the ship closer than 2 km or within Hydroacoustic Search's effective radius (see Spotting Mechanics for additional details). Engine Boost increases the engine power of the destroyer by 8%, increasing its mobility and making it even more difficult to hit - assuming the destroyer has the presence of mind to perform evasive maneuvers and/or duck in and out of islands.