Anti-submarine warfare
Successful ASW operations typically involved a combination of sensor and weapon technologies, along with effective deployment strategies and sufficiently trained personnel.
Common weapons for attacking submarines include torpedoes and naval mines, which can both be launched from an array of air, surface, and underwater platforms.
Accordingly, multiple nations embarked on research into devising more capable ASW methods, resulting in the introduction of practical depth charges and advances in sonar technology; the adoption of the convoy system also proved to be a decisive tactic.
The superpowers of the era constructed sizable submarine fleets, many of which were armed with nuclear weapons; in response to the heightened threat posed by such vessels, various nations chose to expand their ASW capabilities.
The Magnetic Anomaly Detector (MAD), diesel exhaust sniffers, sonobuoys and other electronic warfare technologies also became a staple of ASW efforts.
The first attacks on a ship by an underwater vehicle are generally believed to have been during the American Revolutionary War, using what would now be called a naval mine but what was then referred to as a torpedo.
[7] A similar approach featured a string of 70 lb (32 kg) charges on a floating cable, fired electrically; an unimpressed Admiral Edward Evans considered any U-boat sunk by it deserved to be.
At Admiral John Jellicoe's request, the standard Mark II mine was fitted with a hydrostatic pistol (developed in 1914 by Thomas Firth & Sons of Sheffield) preset for 45 ft (14 m) firing, to be launched from a stern platform.
The U.S. National Research Council, a civilian organization, brought in British and French experts on underwater sound to a meeting with their American counterparts in June 1917.
[citation needed] The first recorded sinking of a submarine by depth charge was U-68, sunk by Q-ship HMS Farnborough off County Kerry, Ireland 22 March 1916.
[17] By early 1917, the Royal Navy had also developed indicator loops which consisted of long lengths of cables lain on the seabed to detect the magnetic field of submarines as they passed overhead.
A number of successful attacks were made,[a] but the main value of air patrols was in driving the U-boat to submerge, rendering it virtually blind and immobile.
[18] However, the most effective anti-submarine measure was the introduction of escorted convoys, which reduced the loss of ships entering the German war zone around the British Isles from 25% to less than 1%.
[22] 211 of the 360 U-boats were sunk during the war, from a variety of ASW methods: This period saw the development of active sonar (ASDIC) and its integration into a complete weapons system by the British, as well as the introduction of radar.
Because the propellers of many submarines were extremely loud in the water[citation needed] (though it doesn't seem so from the surface), range recorders were able to gauge the distance from the U-boat by sound.
Several other technologies were developed; depth sounders that allowed measurement by moving ships were a new innovation, along with a greater appreciation of the properties of the ocean that affected sound propagation.
During 1943, the Allies began to deploy aircraft equipped with new cavity magnetron-based 10-centimeter wavelength radar (ASV III), which was undetectable by "Metox", in sufficient numbers to yield good results.
German subs first had to pass through the highly defended Straits of Gibraltar, where nine were sunk, and a similar number damaged so severely they had to limp back to base.
Instead of commerce raiding like their U-boat counterparts, they followed the Mahanian doctrine, serving in offensive roles against warships, which were fast, maneuverable and well-defended compared to merchant ships.
As the US submarine menace was slight in the beginning, Japanese commanders became complacent and as a result did not invest heavily into ASW measures or upgrade their convoy protection to any degree to what the Allies in the Atlantic did.
Often encouraged by the Japanese not placing a high priority on the Allied submarine threat, US skippers were relatively complacent and docile compared to their German counterparts, who understood the "life and death" urgency in the Atlantic.
However, Japanese destroyer design, tactics, training, and doctrine emphasized surface nightfighting and torpedo delivery (necessary for fleet operations) over anti-submarine duties.
By the time Japan finally developed a destroyer escort, which was more economical and better suited to convoy protection, it was too late; coupled to incompetent doctrine and organization,[c] it could have had little effect in any case.
Late in the war, the Japanese Army and Navy used Magnetic Anomaly Detector (MAD) gear in aircraft to locate shallow submerged submarines.
Nuclear submarines, even faster still, and without the need to snorkel to recharge batteries, posed an even greater threat; in particular, shipborne helicopters (recalling the blimps of World War I)[18] have emerged as essential anti-submarine platforms.
Since the introduction of submarines capable of carrying ballistic missiles, great efforts have been made to counter the threat they pose; here, maritime patrol aircraft (as in World War II) and helicopters have had a large role.
In some areas of the ocean, where land forms natural barriers, long strings of sonobuoys, deployed from surface ships or dropped from aircraft, can monitor maritime passages for extended periods.
Modern MAD arrays are usually contained in a long tail boom (fixed-wing aircraft) or an aerodynamic housing carried on a deployable tow line (helicopters).
At one time, reliance was placed on electronic warfare detection devices exploiting the submarine's need to perform radar sweeps and transmit responses to radio messages from home port.
Fixed-wing aircraft, such as the P-3 Orion & Tu-142 provide both a sensor and weapons platform similar to some helicopters like the Sikorsky SH-60 Seahawk, with sonobuoys and/or dipping sonars as well as aerial torpedoes.
