Destroyer

A destroyer is a type of warship, the nature of which has evolved since it first came into use, roughly at the beginning of the twentieth century. Several other warship designations have, at different times and in different navies, overlapped the "destroyer" role. Most common among these roles are cruiser and frigate. Another type of vessel, whose nomenclature is intertwined with the origin of "destroyer", has been called "torpedo boat", "patrol torpedo (PT)", among other terms.

Initial usage

When the modern self-propelled torpedo was invented, in 1866, by Robert Whitehead, it was initially added to conventional warships, but navies soon realized that a small, fast craft, with a main battery of torpedoes, could threaten much larger warships such as battleships. The battleship of the early 20th century was the largest, most heavily armed, and most heavily protected warship type, but relatively slow and not extremely maneuverable.

Torpedo boats were generally not capable of long-range steaming or being seaworthy in the "blue water" deep ocean; they were coastal craft. When battleships and other large ships, possibly escorting unarmed cargo and troop transports, needed to approach a hostile shore, they needed to deal with the torpedo boat threat. A partial solution was adding a secondary gun battery of smaller caliber, faster firing rate, and faster aiming than the main guns intended to sink other battleships, but the secondary battery still let the torpedo boats come too close.

A new type of vessel, called the torpedo boat destroyer, was developed as an escort to major warships, and possibly merchant vessels threatened by torpedo boats. Such vessels had to be large enough to accompany a battleship on its journey through the blue oceans of the world, but small, fast, and maneuverable enough to pursue and destroy torpedo boats.

First evolution

It soon became obvious that the torpedo boat destroyer was a useful vessel for a wide range of applications, such as convoy escort, so the specialized designation became the simple destroyer. Ironically, while the first destroyers were armed only with quick-firing guns, usually of several calibers from medium to light, navies started equipping destroyers with torpedoes, as the weapon of choice if they did need to confront battleships. For simplicity, the category of "cruiser" is not being included in this immediate discussion; simply assume they were vessels of intermediate characteristics between battleshps and destroyers.

First World War, and a new torpedo threat

The pure torpedo boat was becoming less popular around the start of the First World War, although variants would keep returning. Torpedoes, however, were still a real threat, but from submarines rather than surface vessels.

Technology for finding submerged submarines lagged the introduction of the undersea weapons, and was quite primitive and short-ranged. In general, the first antisubmarine sensors were passive listening devices, called hydrophones. Putting hydrophones on many destroyers allowed an antisubmarine screen to be formed around the "high-value assets", the vessels the submarines had as primary targets.

Once a submerged submarine was located, location being a very loose term at the time, the destroyer needed some way to attack it. Clearly, guns that could blow a surface torpedo boat out of the water were not the answer, since they cannot shoot at underwater targets. The first antisubmarine weapons were depth charges, or containers of explosives that would be dropped, from the surface, over the location of a suspected submarine, and would detonate when they reached a preset depth. The submarine's depth was even harder to determine than its range and bearing (distance) from the destroyer; it was estimated based on the strength of the sound, knowledge of the bottom depth and water characteristics, and a seaman's judgment.

By 1918, however, an active sound-based technique, code-named ASDIC for an apparently nonexistent "Allied Submarine Detection Investigation Committee" was mounted on several British and U.S. destroyers. It came too late for combat use in the First World War, but development actively continued. The more common term became sonar, for "sound detection and ranging". In modern intelligence terminology, active and passive sound-based systems were the acoustic MASINT or acoustic intelligence of geophysical measurement and signal intelligence.

Yet more torpedoes, and things that carried them

By the Second World War, aircraft could drop torpedoes, as well as use weapons including machine guns and bombs. In its evolving role as an escort, as well as being a general-purpose craft for independent assignments, the destroyer now needed to add anti-aircraft warfare to its anti-submarine warfare and anti-surface warfare roles.

Antisubmarine evolution

• hedgehog
• subtypes: destroyer escort, corvette, sloop, frigate

General detection

radar

Antiaircraft evolution

Aircraft, with ever-increasing performance, were more and more of a threat. The initial machine guns quickly proved to have insufficient range and stopping power to be useful, although some .50 caliber or comparable heavy machine guns were retained for final use, and perhaps for attacking boats or to threaten ships with little or no armament. Against non-kamikaze aircraft, the various weapons systems had significantly different effectiveness While some earlier studies showed the .50 caliber as having shot down some aircraft, serious analysis showed that the 20mm Oerlikon autocannon was the lightest weapon with significant kill probability.

Rounds needed to shoot down non-kamikaze aircraft

#aircraft	20mm Oerlikon	40mm Bofors	5"/38 non-proximity	5"/38 proximity fuze
41	30,100	4,500	1,000	550

None, however, were as great a threat as the Japanese kamikaze, essentially the first autonomous anti-shipping missile. The guidance system of these missiles, however, was not electronic, but a human pilot who would die as he crashed the aircraft into its target ship. It was no longer enough to disable the aircraft a distance away from the ship; the destroyer had to force the kamikaze to crash into the sea. Once the kamikaze was in the final approach, even killing the pilot might not stop it from hitting; the final defense had to have sufficient energy to divert the aircraft from its final course.

Rounds needed to shoot down kamikaze aircraft

#aircraft	20mm Oerlikon	40mm Bofors	5"/38 non-proximity	5"/38 proximity fuze
24	27,200	6,000	1,000	200

The problem was not firepower alone, but also fire control. Ideally, a destroyer could engage kamikazes with 5" guns, equipped with proximity fuzes. These guns had the greatest range and killing power, and best integration with the CIC and radar.

Surface warfare evolution

• Destroyer leader
• Long Lance torpedo

Information-centric warfare

Still in WWII, the destroyer, along with other warships, began to regard information as a weapon. The captain of a destroyer might be more effective in combat not on high on the bridge, relying on his eyes and ears, but in a combat information center, where lookout reports, sonar, radar, radio messages, and other data could be fused onto tactical charts.

The dawn of guided missiles

Destroyers and cruisers were the first warships, in most navies, to be equipped with guided missiles. The initial installations were usually surface-to-air missiles, sometimes with a secondary surface attack capability.

Dedicated surface-to-surface missiles, specifically anti-shipping missiles intended for use against targets surrounded by water, revived the concept of the "eggshell with a sledgehammer", or small fast vessel with a powerful offensive weapon. In the revival, however, the sledgehammer was the naval surface-to-surface missile (SSM).

In the first combat use of an anti-shipping SSM, Egyptian Osa-class missile boats, of Soviet design and construction, sank the Israeli Navy flagship, the destroyer Eilat during the 1967 Arab-Israeli War. The Osas used P-15 Termit (NATO reporting name SS-N-2 STYX) missiles.

Modern destroyers

Even now, the role changes. A Burke-class destroyer of the U.S. or Japanese navies still has a 5" gun and smaller autocannon, but its main battery is a vertical launch system that can fire a variety of precision-guided munitions. The latest "flight 2B" Burkes also have a pair of helicopters, and the AEGIS battle management system. The vessel has the displacement of a WWII light cruiser.

Anti-air warfare

This is the most potent mission on modern destroyers, although its surface-to-air missiles usually have a secondary surface-to-surface capability, and the same launchers used for the SAMs can fire surface-to-underwater missiles and surface-to-surface missiles.

Anti-submarine warfare

Given that the most potent torpedoes are now on submarines, not surface ships, a destroyer will want to engage a submarine at a considerable distance. If the destroyer carries an antisubmarine helicopter, the role of the ship may be to support the helicopter, with sensors and refueling. The kill mechanism would be lightweight torpedoes dropped from the helicopter.

If the destroyer has a long-range surface-to-underwater missile that will fly through the air and drop a homing torpedo in the predicted vicinity of the submarine, it may be just as much a threat as the helicopter. Indeed, the helicopter may emphasize its sensors for finding the submarine and letting the destroyer's SUMs kill it.

Destroyers have non-missile carried torpedoes, but these are last-resort weapons, generally to kill a submarine that has already fired torpedoes that will kill the destroyers. The new Russian torpedoes of extremely high, even supersonic, speed may put a new dimension on this tactical scenario.

Anti-surface warfare

Different navies give their destroyers different priorities. The later Burke class have done away with their pure Harpoon anti-shipping missiles, but the Russian Sovremenny class and the Chinese equivalent carry the very potent Moskit (NATO designation SS-N-22 SUNBURN).

Although its mission is no longer primarily surface warfare, it could give a WWII battleship a very hard time with its RIM-66 Standard missiles in surface-to-surface mode, using over-the-horizon targeting. A 13.5" diameter missile, of a weight depending on how much fuel it consumed, traveling at Mach 3.5, would have more kinetic energy than a traditional battleship shell, to say nothing of a substantial high-explosive warhead and burning fuel.

Support to land operations

• cruise missile
• autocannon, including advanced gun systems and futures such as vertical gun systems and railguns