Anti-submarine warfare
The first recorded attack by an underwater vehicle occurred during the American Revolutionary War, using what was then called a torpedo but is now known as a naval mine. This early weapon marked the beginning of a centuries-long struggle to counter threats from beneath the waves. By 1866, British engineer Robert Whitehead had invented the first effective self-propelled torpedo, which changed the nature of naval warfare forever. The Nordenfelt I submarine followed shortly after in 1884-1885, becoming the first vessel equipped with such a weapon.
Navies struggled for decades to develop any means of detecting submerged vessels. During the First World War, attacks on U-boats were limited to damaging their periscopes with hammers or deploying explosive grapnel sweeps. HMS Vernon, the Royal Navy torpedo establishment, studied these methods and successfully sank four or five U-boats using them. Other approaches included floating cables strung with charges fired electrically, though Admiral Edward Evans dismissed any success achieved this way as undeserved.
Hand-thrown guncotton bombs and the Lance Bomb became common tools before more sophisticated systems emerged. The Lance Bomb featured a cone-shaped steel drum mounted on a shaft, designed to be thrown directly at a submarine. Aircraft began dropping bombs attached to lanyards that would trigger charges upon impact. These early depth charge Type A devices worked effectively at distances around one hundred feet, despite frequent issues with lanyards tangling and failing to function properly.
During June 1915, the Royal Navy began operational trials of the Type D depth charge, which contained a charge of TNT or amatol when supplies became critical. This weapon could fire at depths between fifty and three hundred feet, proving effective against submerged targets. By July 1917, depth charges had evolved to settings allowing detonation at various depths, a design that remained largely unchanged through the end of World War II.
The British Admiralty established the Board of Invention and Research in July 1915 to evaluate suggestions from the public and conduct their own investigations. Some fourteen thousand suggestions were received about combating submarines during this period. In December 1916, the Royal Navy created its Anti-Submarine Division, which later gave rise to the term Asdic for sonar technology. Relations between this division and the Board of Invention and Research remained poor throughout much of the war.
Indicator loops consisting of long lengths of cable laid on the seabed detected magnetic fields as submarines passed overhead. These guard loops used controlled mines that could be detonated from shore stations once a swing appeared on the galvanometer. The first recorded sinking of a submarine by depth charge occurred on the 22nd of March 1916, when U-68 was destroyed off County Kerry, Ireland by Q-ship Cushing. Seaplanes and airships also patrolled for submarines, though their main value lay in driving U-boats to submerge and render them virtually blind.
Throughout the Second World War, Allied radar technology proved far superior to German counterparts, giving surface ships and aircraft crucial advantages over U-boats. By the second half of 1942, the Metox radar detector allowed U-boats some warning against airborne attacks, but this advantage disappeared when Allies deployed cavity magnetron-based ten-centimeter wavelength radar known as ASV III during 1943. Eventually, the Naxos radar detector fielded by Germany could detect ten-centimeter wavelength radar, yet it offered only very short range and limited time for U-boats to dive before detection.
Between 1943 and 1945, radar-equipped aircraft accounted for the bulk of Allied kills against U-boats, marking a turning point in the Battle of the Atlantic. The Leigh Light, an airborne searchlight used in conjunction with radar, surprised and attacked enemy submarines on the surface at night. This combination forced U-boats to remain submerged, disrupting their patrols and attack runs. Commanders like F.J. Johnnie Walker developed integrated tactics that made hunter-killer groups practical propositions, allowing one destroyer to track while another attacked.
Intelligence efforts played a major role in curtailing submarine threats, particularly through breaking German Naval Enigma codes at Bletchley Park. Information gathered this way was dubbed Ultra and enabled tracking of U-boat packs to allow convoy re-routings. When Germans changed their codes or added a fourth rotor to Enigma machines in 1943, convoy losses rose significantly. By war's end, Allies regularly broke and read German naval codes, giving them decisive advantages in protecting shipping lanes.
Nuclear submarines posed even greater threats than diesel-electric vessels because they required no snorkeling to recharge batteries and could maintain high speeds indefinitely. Shipborne helicopters emerged as essential anti-submarine platforms during the 1960s, capable of operating from almost any warship and equipped with ASW apparatus. Increasingly capable fixed-wing maritime patrol aircraft covered vast areas of ocean, complementing these helicopter operations.
The Magnetic Anomaly Detector became a staple of post-war ASW efforts, using Earth's magnetosphere to detect anomalies caused by large metallic vessels like submarines. Modern MAD arrays were contained in long tail booms on fixed-wing aircraft or aerodynamic housings carried on deployable tow lines for helicopters. Keeping sensors away from engines and avionics helped eliminate interference from carrying platforms. Sonobuoys and other electronic warfare technologies also became standard equipment for detecting submerged targets.
Dedicated attack submarines purpose-built to track down and destroy other submarines became key components of modern navies. Torpedo-carrying missiles such as ASROC and Ikara represented another area of advancement, combining ahead-throwing capability with longer-range delivery systems. These developments responded directly to heightened threats posed by nuclear-powered vessels armed with ballistic missiles that increased submarine lethality dramatically.
Acoustics remain particularly important in active and passive sonar systems, along with sonobuoys and fixed hydrophones aiding detection of radiated noise. Sonar can be mounted on hulls or deployed in towed arrays to maximize coverage and effectiveness. Pyrotechnics including markers, flares, and explosive devices support search operations by marking locations or creating distractions. Searchlights and radar help identify surfaced parts of submarines while high frequency radio direction finding determines bearings of U-boats.
Hydrodynamic pressure wave wake detection allows identification of Kelvin wakes generated by submarines below depths of one hundred meters. Submarines may still generate internal wakes detectable from the surface even when operating deeper than this threshold. Laser detection and ranging systems track surfaced vessels using optical and satellite imagery. Electronic countermeasures include noise makers and bubble generators designed to confuse acoustic sensors.
Forward looking infrared detectors now track large plumes of heat that fast nuclear-powered submarines leave while rising to the surface. FLIR devices also see periscopes or snorkels at night whenever submariners might be incautious enough to probe the surface. Magnetic anomaly detection continues serving as a passive device for identifying submerged threats across vast ocean areas. Bottom-mounted hydrophones process data from land-based stations to monitor maritime passages for extended periods.
Neutralizing ballistic missile submarines remains a key driver for modern anti-submarine warfare capabilities because these vessels pose existential threats through nuclear blockades. Maritime patrol aircraft and helicopters play large roles in countering such threats, covering vast distances and maintaining constant surveillance over strategic waterways. The development of dedicated attack submarines called hunter-killers became strongly influenced by duels between opposing naval powers seeking dominance beneath the waves.
Climate change may decrease submarine detectability in certain locations according to a 2024 study, adding new challenges to existing ASW strategies. Nations continue developing seabed listening devices capable of tracking submarines across southern Indian Ocean regions from South Africa to New Zealand. Some SOSUS arrays have been turned over to civilian use for marine research while others remain active military assets protecting national interests.
Anti-submarine missiles give flexibility in terms of launch platforms, with countries like India developing supersonic long-range systems such as SMART that deliver torpedoes up to six hundred forty-three kilometers away. Satellites image sea surfaces using optical and radar techniques to identify potential threats before they can strike. Surface ships maintain importance due to endurance and towed array sonars, while submarines themselves serve as main ASW platforms because of their ability to change depth and operate quietly.
Common questions
When did the first recorded attack by an underwater vehicle occur?
The first recorded attack by an underwater vehicle occurred during the American Revolutionary War. This early weapon was then called a torpedo but is now known as a naval mine.
Who invented the first effective self-propelled torpedo in 1866?
British engineer Robert Whitehead invented the first effective self-propelled torpedo in 1866. This invention changed the nature of naval warfare forever and led to vessels like the Nordenfelt I submarine being equipped with such weapons shortly after.
What date marked the first recorded sinking of a submarine by depth charge?
The first recorded sinking of a submarine by depth charge occurred on the 22nd of March 1916. U-68 was destroyed off County Kerry, Ireland by Q-ship Cushing using this method.
How did radar technology change anti-submarine warfare during World War II?
Allied radar technology proved far superior to German counterparts throughout the Second World War. By 1943, cavity magnetron-based ten-centimeter wavelength radar known as ASV III gave surface ships and aircraft crucial advantages over U-boats.
When were shipborne helicopters established as essential anti-submarine platforms?
Shipborne helicopters emerged as essential anti-submarine platforms during the 1960s. These aircraft are capable of operating from almost any warship and are equipped with ASW apparatus to detect submerged targets.