The attempt to locate and track submarines in order to
neutralize them before they are able to deploy weapons, discharge passengers or
payload, or conduct surveillance. This endeavor is currently fulfilled by
surface vessels, aircraft, satellites, submerged electronic barriers, naval
intelligence, and other submarines.
The efficacy of a vessel capable of operating beneath the
surface of the ocean had been recognized for centuries, and a submersible did
prove it was capable of destroying a surface ship when the Confederate vessel
H. L. Hunley sank the Union warship Housatonic with a spar torpedo on 17
February 1864. It was not until the late nineteenth century, however, that
truly practical submarines first emerged, notably the types designed by John
Holland. When the self-propelled torpedo was united with the submarine, first
accomplished in an external tube aboard the Swedish-designed Nordstrom 1 in
1882, the major offensive capability of the submarine was established for the
next seven decades. Torpedoes improved in stability, performance, and explosive
power, and soon submarine designs included internal torpedo tubes.
Although the devastating potential of submarines against
shipping was noted by some naval officers in policy positions, the early
submarines were fragile and thus their presence did not set off a general alarm.
The first submarines, being slow, of short range, mechanically unreliable, and
difficult to maneuver, did not pose a great threat to much faster and more
heavily armed surface ships. In addition, a few British naval theorists
believed that submarines would not be deployed in a war because of prohibitions
against using weapons of stealth that went against common agreements of how
wars were conducted.
The relatively cheap cost of submarines and their improved
performance in shallow coastal waters, such as the English Channel and the
Mediterranean, made submarines an attractive option for countries that wished
to challenge large navies such as Great Britain’s but lacked resources to
support an equivalent navy financially or logistically. In the early twentieth
century the submarine became a common naval weapon, and measures to counter
these vessels were sought.
The transmission of sound through water was well known by
the time submarines first appeared, and it was not long before various
underwater listening devices, hydrophones, were employed to pick up the sounds
of submarines beneath the surface. Hydrophones constituted a passive system
that did not provide information on bearing or range, however. They were also
subject to interference from the sounds emanating from the host ship itself.
The first exercises officially sanctioned to demonstrate ASW
techniques were conducted by the British in 1904; the chief strategy was to
attempt to come alongside a submarine and attach an explosive. Nets were also
used to snare submarines, but these proved impractical. An aircraft was
employed to spot a submarine in 1912, a harbinger of a very successful ASW
technique.
At the onset of World War I, all the leading naval powers
deployed submarines. On 11 August 1914, the British light cruiser Birmingham
sliced in half the German submarine U-15, the first submarine casualty of the
war. On 5 September, the U-21 became the first submarine to destroy an enemy
vessel and survive when it torpedoed and sank the British cruiser Pathfinder.
But it was the obsolete paraffin-powered U-9 that forced Britain to consider
its ASW tactics carefully. On 22 September 1914, this U-boat torpedoed and sank
the three old British cruisers Aboukir, Hogue, and Cressy in quick succession,
with heavy loss of life.
ASW during World War I foreshadowed the kinds of techniques
and weapons deployed in the next world war, but ASW remained generally
ineffective compared to the destruction caused by submarines. One of the first
ASW measures was to have ships steam in a zigzag pattern at top cruising
speeds, making it difficult for submarines to predict a ship’s course and hence
calculate where to fire a torpedo.
Disruptive camouflage schemes also helped disguise the
direction, speed, and type of vessel as seen from the low vantage of a
submarine periscope or conning tower. Antitorpedo nets were deployed, but these
proved less than satisfactory. Q-ships, armed vessels outfitted as merchantmen
in order to lure unsuspecting submarines within gunfire range, were utilized
with some success, although submarines soon resorted to simply destroying any
merchant ship so as not to risk falling victim to this ruse. Ramming surfaced
submarines was also a standard ASW technique of the period and accounted for 19
U-boats sunk.
Submarines proved to be good hunters themselves, with
British submarines destroying 18 German U-boats. Depth charges were first
deployed in January 1916, but it was not until 1917 that a satisfactory charge
was perfected. These devices were rolled off the sterns of surface ships, but
projectors mounted on a ship’s deck soon appeared to launch them in precise
patterns from the ship. Destroyers, originally designed to counter torpedo
boats, now became associated with ASW since they were fast, highly maneuverable,
and could unload depth charges without much disruption of their deck plans or
stability.
The most effective ASW weapon of World War I, however, was
the submerged mine, usually deployed in high-density barriers. The Allies sowed
them at varying depths and in great numbers, most notably in the North Sea
barrage. This was designed to make a submarine’s transit from Germany to the
Atlantic extremely risky. Choke points in the English Channel were also
employed. Mines accounted for the sinking of at least 75 U-boats.
Despite these techniques, German U-boats continued to sink
Allied ships at alarming rates, and only the belated introduction of the convoy
system enabled Britain to survive. It proved the best defense against
submarines and became the most reliable ASW measure of the war.
Once shipping was satisfactorily protected through convoys,
Allied ships and planes were free to pursue U-boats with improved ASW weapons
and techniques, including more active use of hydrophones. Torpedoes remained
highly effective, but submarines ironically destroyed most unarmed merchant
shipping with their heavy-caliber deck guns while surfaced; once submerged,
submarines were less effective because of their slower speed and poor
endurance. Hence they only resorted to underwater approaches when there was a
threat from armed surface vessels. If a submarine could be located and forced
under, shipping could more readily be protected.
The war ended before early ASDIC (sonar) sets could be
deployed, but these instruments demonstrated great potential for recognizing
submarines beneath the water as well as for providing range and bearing.
The success of sonar led in the interwar period to
complacency about the need for further ASW research, since echo-ranging
appeared to compromise a submarine’s ability to remain undetected. The fact
that most submarine attacks had actually occurred on the surface, where sonar
was irrelevant, was not taken into consideration. Submarines of World War II
were faster, able to sustain greater depths, and had longer range and more
powerful weapons than submarines of the previous world war.
With the beginning of World War II in September 1939, German
submarines were once again deployed around Great Britain. They were not charged
with destroying shipping, but rather with attacking naval vessels. Over the
course of the next year, however, the rules of engagement were expanded and
U-boats began concerted efforts against shipping. The Allies instituted convoy
tactics at the onset of hostilities, but the fall of Norway, the Low Countries,
and France in 1940 gave German U-boats better access to the Atlantic convoy
lanes, something conspicuously missing during the last war. This greatly
expanded the area where submarine attacks could be expected.
Increasing numbers of Allied escort vessels, long-range
aircraft, and small carriers to accompany convoys infringed upon submarines’
ability to attack shipping. Depth charges and launchers became more reliable
and powerful. Sonar also greatly improved, and was ultimately able to determine
a submarine’s approximate bearing and depth. Such information could be
exploited by the newly invented ahead-throwing weapons, the hedgehog and squid.
Airborne ordnance, including sonobuoys, homing torpedoes, and devices such as
the magnetic anomaly detector (MAD), were becoming commonplace.
Radar, both on surface ships and in aircraft, proved the
most important ASW device of the war; radio direction finding (HF/DF) was also
extremely important against German submarines. Decoded intelligence also played
a major role in the defeat of the U-boats. Whole convoys could be routed around
known German wolf packs, while hunter-killer groups composed of escort
carriers, destroyers, and destroyer escorts could intercept and sink U-boats.
Germany developed countermeasures, but the sheer scale of Allied saturation
techniques, combined with the extraordinary production of shipping, made it
very difficult for diesel submarines to prosecute the war.
In the Pacific, American submarines waged an even more
destructive war against Japanese shipping. Japanese ASW was markedly inferior
to that of the Allies, partly as a result of deeply ingrained doctrine that
submarines were fleet vessels and deployed only against other naval ships, not
merchant ships. Consequently, the Japanese navy had few ASW measures to protect
shipping in place before their 7 December 1941 attack on Pearl Harbor.
Following the war, true submersibles appeared, thanks to
inventions such as the snorkel. These allowed submarines to operate at high
speeds beneath the ocean surface for extended periods of time and be equipped
with long-range weapons. This completely redefined ASW. It changed from
defending and preventing submarine attacks on shipping or reducing the
effectiveness of a submarine’s weapons once fired to active early detection of
submarine movements at sea. The primary objective of a modern submarine
equipped with nuclear or air independent propulsion (AIP) and carrying nuclear
ballistic missiles is to avoid contact so that it can remain part of a
strategic force.
Antishipping patrols are no longer the primary task of
submarines and, although that capability remains part of their role, their
overriding offensive objective is to deliver nuclear and nonnuclear warheads to
targets at great distances. Therefore, current ASW is chiefly charged with
close monitoring of submarine movements rather than the protection of resources
at sea. Radar would be ineffective against submarines that remained underwater
for much of their patrols; MAD had short range, and sonar found it more
difficult to obtain targets and bearing on increasingly quiet and fast
submarines. Surface ships would have difficulty prosecuting contacts made at
any distance at the necessary speed; therefore, aircraft—both fixed wing and
helicopters—and missiles would have to be deployed.
This German technology was incorporated into both the
Russian and western navies, with the newly created NATO preparing for a large
Soviet submarine fleet that might attack western sea lanes en masse. Early on
it was recognized that it would be easier to track submarines close to their
bases than at sea, so barriers close to bases that could provide data on
submarine movements or potentially lethal obstructions became an integral part
of postwar ASW.
A guided missile was first launched from a submarine in
1947, but submarines had to surface in order to fire these weapons. The first
nuclear-powered submarine, the U.S. Navy’s Nautilus, was commissioned in 1954,
and was quickly followed by similar USSR submarines. Nuclear power enabled
submarines to cruise for weeks at a time without surfacing—a major tactical
advantage.
The first successful launch of a ballistic missile from a
submerged submarine occurred in July 1960, thereby radically revising ASW requirements
in less than 15 years from the end of World War II. The chief objective of ASW
remained the early and accurate detection of submarines, although the timing
had now changed. Given the vast destructive power of a single submarine, it
became paramount for ASW to prevent a submarine from achieving weapon launch.
The primary western ASW strategy remained containment, achieved through
barriers such as SOSUS, a network of hydrophones placed at key areas along the
ocean floor; long-range air patrols capable of deploying sonobuoys and improved
MAD devices; Atlantic and Pacific distant early warning (DEW) lines that
stationed radar-equipped ships at key points far at sea; specialized
hunter-killer submarines lurking near bases in order to detect and tail submarines
as they began a patrol (as revealed through intelligence information); and
prosecution upon detection, which required fast, long-range weapons capable of
destroying a submarine before it would be able to respond.
Rocket-launched homing torpedoes fired from surface ships
(ASROC) or submarines (SUBROC) were developed and deployed. The number of
vessels and aircraft necessary for continual monitoring of the Soviet submarine
fleet was achieved through multiple nation participation, upgrading equipment of
existing ships, and large expenditures on production of new aircraft,
helicopters, and submarines. Very long-range, low-frequency sonars, capable of
fitting into or being towed by submarines and surface ships, were also
developed that increased their ability to detect enemy submarines at great
distances.
The Cold War was the high point of large-scale ASW tactical
and weaponry development. The end of the war has reduced the likelihood of a
massive underwater attack for the moment, but ASW remains one of the most
important tasks of modern navies, since a single submarine—perhaps at the
behest of a rogue state—can have immense destructive power, capable of
threatening any spot on the globe.