|Mark 24 mine|
Mark 24 acoustic torpedo
|Place of origin||United States, Canada, United Kingdom|
|Used by|| United States Navy |
Fleet Air Arm
Royal Canadian Navy
|Wars||World War II|
|Designer|| Western Electric Company |
Bell Telephone Laboratories
Harvard University Underwater Sound Laboratory
|Manufacturer|| General Electric Company |
Western Electric Company
|Effective firing range||4000 yards|
(10 minutes search duration)
|Warhead weight||92 pounds|
|Mk 142 fuze, contact exploder|
|Engine||Electric, secondary battery|
|preset circle search, passive acoustic|
The Mark 24 mine (also known as FIDO or Fido) is an air-dropped passive acoustic homing anti-submarine torpedo used by the United States during the Second World War. It entered service in March 1943 and remained in use with the US Navy until 1948. Approximately 4,000 torpedoes were produced, with 204 ultimately being deployed during the war. As a result of its use, 37 Axis submarines were sunk and a further 18 were damaged. The torpedo was also supplied to the British and Canadian forces. The deceptive name of "Mark 24 Mine" was deliberately chosen for security purposes, to conceal the true nature of the weapon.
A submarine is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. It is also sometimes used historically or colloquially to refer to remotely operated vehicles and robots, as well as medium-sized or smaller vessels, such as the midget submarine and the wet sub.
A modern torpedo is a self-propelled weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with its target or in proximity to it.
The Axis powers, also known as "Rome–Berlin–Tokyo Axis", were the nations that fought in World War II against the Allies. The Axis powers agreed on their opposition to the Allies, but did not completely coordinate their activity.
The concept of a torpedo which would "home" on its target had been studied by torpedo designers as far back as the first World War. While the concept was highly interesting, implementation had to await a better understanding of the physics of sound generation and transmission in the sea and the development of the technology from which such a torpedo could be designed and constructed. During World War II, German submarines were equipped with electrically driven acoustic homing torpedoes which had started development as far back as 1933. The Falke T-4 and Zaunkoenig T-5 torpedoes entering service in 1943 were designed to attack surface ships and ran at a preset depth. A similar torpedo (MK28) entered US submarine service in 1944.
The G7e or more appropriately the G7e/T2, G7e/T3, and G7e/T4 Falke torpedoes were, with the exception of the T4 model, the standard torpedoes for Germany during World War II. All of the G7e models shared standardized dimensions for all German torpedoes designed for use by U-boats during World War II, they measured 53.3 cm (21 inches) in diameter, 7.16 m in length, and carried a Schießwolle 36 warhead of 280 kg. All were powered by 100 hp (75 kW) electric motors and lead-acid batteries which needed constant maintenance to maintain their reliability. Additionally, the batteries of these torpedoes needed to be preheated to a temperature of 30 °C (85 °F) to operate with maximum speed and range, though generally this was a non-issue as U-boats had the element of surprise and often had the advantage of firing the first shot.
The G7es (T5) "Zaunkönig" ("wren") was an acoustic torpedo employed by German U-boats during World War II. It was called the GNAT by the British.
While effective against surface ships, the MK28 was of limited use against submarines, due to its inability to track and adjust to changes in both depth and azimuth. The design of Fido enabled it to meet the size, weight, and aerial launch specifications associated with air-drop water entry, in addition to addressing the shortcomings of earlier torpedo tracking and control systems.
The US Navy began studies into an air-dropped anti-submarine torpedo in the autumn of 1941. Based on a formal set of requirements, Harvard Underwater Sound Lab (HUSL) and Bell Telephone Labs began development in December 1941. These projects later became Office of Scientific Research and Development project 61 (FIDO).
Nokia Bell Labs is an industrial research and scientific development company owned by Finnish company Nokia. Its headquarters are located in Murray Hill, New Jersey. Other laboratories are located around the world. Bell Labs has its origins in the complex past of the Bell System.
Both Bell Labs and HUSL proceeded with parallel development of torpedoes, with a complete exchange of information between them. Western Electric were to develop a lightweight, shock resistant, 48 volt lead-acid battery capable of providing 110 amps for 15 minutes. General Electric were to design and fabricate propulsion and steering motors and to investigate an active acoustic homing system. David Taylor Model Basin was to assist with hydrodynamics and propulsion.
Western Electric Company was an American electrical engineering and manufacturing company that served as the primary supplier to AT&T from 1881 to 1996, and to the local Bell Operating Companies until 1984. The company was responsible for many technological innovations and seminal developments in industrial management. It also served as the purchasing agent for the member companies of the Bell System.
General Electric Company (GE) is an American multinational conglomerate incorporated in New York City and headquartered in Boston. As of 2018, the company operates through the following segments: aviation, healthcare, power, renewable energy, digital industry, additive manufacturing, venture capital and finance, lighting, and oil and gas.
The David Taylor Model Basin (DTMB) is one of the largest ship model basins—test facilities for the development of ship design—in the world. DTMB is a field activity of the Carderock Division of the Naval Surface Warfare Center.
The guidance system consisted of four hydrophones placed around the midsection of the torpedo, connected to a vacuum tube-based sound processing array. A Bell Labs proportional navigation and HUSL non-proportional steering system had been demonstrated by July 1942.
In electronics, a vacuum tube, an electron tube, or valve or, colloquially, a tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
Proportional navigation is a guidance law used in some form or another by most homing air target missiles. It is based on the fact that two vehicles are on a collision course when their direct Line-of-Sight does not change direction as the range closes. PN dictates that the missile velocity vector should rotate at a rate proportional to the rotation rate of the line of sight, and in the same direction.
An existing Mark 13 torpedo provided the body of the torpedo, it was modified by shortening the hull, reducing the diameter, reducing the weight, and designing a hemispherical nose section to carry the explosive charge, and a conical tail section with four stabilizing fins and rudders and a single propeller. The effect of these modifications was to produce a relatively short, "fat" torpedo.
The Mark 13 torpedo was the U.S. Navy's most common aerial torpedo of World War II. It was the first American torpedo to be originally designed for launching from aircraft only. They were also used on PT boats.
In June 1942, the US Navy decided to take the torpedo into production, even though there was still major testing work remaining on the project, including air-drop testing. The Bell Labs version of the guidance system was selected for production, with proportional homing. Testing of the pre-production prototypes continued on into December 1942, and the US Navy received the first production models in March 1943.
Initially 10,000 torpedoes were ordered, but FIDO proved so effective that the order was reduced to 4,000. The torpedoes ended up costing $1,800 each.
Upon water entry, FIDO performed a circular search at a predetermined depth controlled by a bellows and pendulum system. This continued until the potential target's 24 kHz acoustic signal detected by the hydrophones exceeded a predetermined threshold level, at which point control was then shifted to the passive acoustic proportional homing system. Initially the torpedoes were set to search for a target at a depth of 50 feet (15 m), this was later changed to 150 feet (45 m). To prevent the torpedo accidentally attacking surface ships, it resumed its circling search if it rose above a depth of 40 feet (12 m).
The torpedo's relatively low speed was kept secret because, although U-boats could not outrun the torpedo when submerged, they could outrun it on the surface.
On 14 May 1943 a Catalina of the US Navy attacked and destroyed a U-boat; this was either U-657or U-640. On 13 May an RAF Coastal Command Liberator B/86 had attacked a U-boat with a FIDO, but this vessel, U-456, was only damaged, sinking the following day from damage received. One of these vessels was the first U-boat sinking achieved using FIDO. During its career, the torpedo sank a total of 37 submarines, achieving an effectiveness of about 22%, compared with about 9% for depth charges.
from US Navy OEG Study No. 289, 12 August 1946 provides the following data related to Mark 24 effectiveness:
|Number of attacks in which Mark 24s were launched||264|
|Total number of Mark 24 torpedoes launched - all targets||340|
|Number of Mark 24s launched against submarines||204|
|Number of Mark 24 attacks on submarines by US aircraft||142|
|Number of Mark 24 attacks by Allied (primarily British) aircraft||62|
|Number of German U-boats sunk by FIDO||31|
|Number of German U-boats damaged by FIDO||15|
|Number of Japanese submarines sunk by FIDO||6|
|Number of Japanese submarines damaged by FIDO||3|
|Total number of submarines sunk by FIDO (German & Japanese)||37|
|Total number of submarines damaged||18|
Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation, and SODAR is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.
U-boat is an anglicised version of the German word U-Boot [ˈuːboːt] (
An anti-submarine weapon (ASW) is any one of a number of devices that are intended to act against a submarine and its crew, to destroy (sink) the vessel or reduce its capability as a weapon of war. In its simplest sense, an anti-submarine weapon is usually a projectile, missile or bomb that is optimized to destroy submarines.
The Sting Ray torpedo is a current British acoustic homing light-weight torpedo (LWT) manufactured by GEC-Marconi, who were later bought out by BAE Systems. It entered service in 1983.
An acoustic torpedo is a torpedo that aims itself by listening for characteristic sounds of its target or by searching for it using sonar. Acoustic torpedoes are usually designed for medium-range use, and often fired from a submarine.
A towed array sonar is a system of hydrophones towed behind a submarine or a surface ship on a cable. Trailing the hydrophones behind the vessel, on a cable that can be kilometers long, keeps the array's sensors away from the ship's own noise sources, greatly improving its signal-to-noise ratio, and hence the effectiveness of detecting and tracking faint contacts, such as quiet, low noise-emitting submarine threats, or seismic signals.
Anti-submarine warfare is a branch of underwater warfare that uses surface warships, aircraft, or other submarines to find, track, and deter, damage, or destroy enemy submarines.
The Mark 37 torpedo is a torpedo with electrical propulsion, developed for the US Navy after World War II. It entered service with the US Navy in the early 1950s, with over 3,300 produced. It was phased out of service with the US Navy during the 1970s, and the stockpiles were sold to foreign navies.
An aerial torpedo, airborne torpedo or air-dropped torpedo is a naval weapon, a torpedo, that an aircraft—fixed-wing aircraft or helicopter—drops in the water, after which the weapon propels itself to the target. First used in World War I, air-dropped torpedoes were used extensively in World War II, and remain in limited use. Aerial torpedoes are generally smaller and lighter than submarine- and surface-launched torpedoes.
The APR-3E airborne light ASW acoustic homing torpedo is designed by Russian Tactical Missiles Corporation JSC to engage current and future submarines in at depth from the surface down to 800 metres at speed of up to 43+ knots, and it is a replacement for earlier APR-2 light antisubmarine acoustic homing torpedo.
German submarine U-402 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II.
The Mark 10 torpedo was a torpedo put into use by the United States in 1915. It was derived from the Mark 9 aircraft torpedo converted to submarine use. It was used as the primary torpedo in the R- and S-class submarines. It used alcohol-water steam turbine propulsion. It was succeeded by the problematic Mark 14 torpedo, but remained in service in S-boats & fleet submarines through the Pacific War. The Mark 10 featured the largest warhead of any U.S. torpedo developed at that time. Stockpiles of Mark 10 Mod 3 torpedoes were used extensively during the first part of World War II due to short supply of the newer and longer (246 in Mark 14s, with some fleet submarines carrying a mixture of both types on patrol.
German submarine U-422 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II.
German submarine U-467 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II.
The Mark 21 Mod 2 torpedo, was a passive acoustic homing variant of the Mark 13 torpedo. It used the widely-used Mark 13 torpedo as a basis, with the addition of passive acoustic homing developed by Bell Labs.
A nuclear torpedo is a torpedo armed with a nuclear warhead. The idea behind the nuclear warheads in a torpedo was to create a much bigger and more explosive blast. Later analysis suggested that smaller, more accurate, and faster torpedoes were more efficient and effective.