NT-37
The NT-37 medium-weight torpedo is an extensively reworked Mk 37 torpedo that is in service with several navies. It can be launched from surface ships or submarines. Alliant has offered several versions of the NT-37, including the digital NT-37E and the analog NT-37F.
The NT-37E proved to be too expensive for most prospective retrofit candidates. The costly strap-down guidance system provides more precision than the torpedo needs to get close enough for its terminal homing system. Therefore, Alli-ant claims that the NT-37F, which upgrades the analog system with gimballed gyros, achieves nearly the same performance and is more reliable than earlier Mk 37s while avoiding the expense of the digital system.
VARIANTS •
NT-37C was developed in the early 1970s as an upgrade of the older Mk 37 torpedo. An Otto-fuel piston motor like that of the Mk 46 replaced the Mk 37′s electric motor and battery. NT-37D used the NT-37C motor and replaced vacuum-tube acoustic technology with a solid-state acoustic processor system designed to improve antiship capability as well as doubling acoustic performance against submarine targets.
NT-37E replaces vacuum-tube analog guidance and control with strap-down solid-state digital equipment using Xylog processors and inertial navigation. Fitted with two-way communications link through the guidance wire. Improvements doubled the active detection range and nearly doubled the passive range. Reliability and logistical support also upgraded.
NT-37F was introduced in 1990 as a less expensive retrofit of Mk 37s. Original
control system replaced by upgraded analog system controlled by computer having Intel 80186 processors; senses drift of less than one knot. After launch and immediately before turning on its homing sensor, the NT-37F takes background noise readings of itself and surrounding medium and can adjust seeker sensitivity accordingly.
The designation NT-37F is trademark-protected.
DEVELOPMENT •
NT-37C/D kits developed and manufactured by Northrop Corp. from 1968 to 1980, achieving initial operational capability in 1974. The NT-37E/F developed by Honeywell Marine Systems (later Alliant Techsystems) in Everett, Washington. The NT-37E seeker was first tested in 1980, full kit tested in 1982-83.
Not in service in US ships but has replaced Mk 37 in several other navies. Canada, Norway, Peru, and Taiwan operated earlier NT-37 torpedoes; Israel (in 1986), Netherlands, and Taiwan also procured
NT-37Es. Egypt (1991) was the first customer for the NT-37F.
SPECIFICATIONS •
weight wire-guided 1,653 lb (750 kg),
free-running 1,415 lb (642 kg)
warhead 331 lb (150 kg) dimensions
length wire-guided 14 ft 9 in
(4.5 1 m) , free-running
12 ft 7 in (3.85 m)
diameter 19 in (485 mm) warhead conventional high explosive guidance solid-state acoustics designed to improve anti-surface-ship capability; solid-state, computer-driven guidance and control (NT-37E is strap-down digital, NT-37F is analog with gimballed gyros); three search patterns: straight run (antiship), straight run with acoustic reattack, snake and circle, active for ASW, passive for antiship
POWERPLANT 90-hp thermochemical rotary piston cam motor using liquid monopropellant (Otto) fuel
SPEED 2 speeds selectable, max range
9.7 nm (11.2 mi; 18 km) Mk 46 lightweight torpedo
The Mk 46 is the most widely deployed 12.75-in (324mm) lightweight torpedo for use against submarines by helicopters, aircraft, and surface ships; it is also fitted in the Captor deep-water mine.
Development of the Mk 46 in the late 1950s as a successor to the Mk 44 addressed a design goal of a lightweight torpedo to counter nuclear-propelled submarines. Speed and range demands led to the substitution of a chemical-fuel motor in place of the Mk 44′s battery-powered electric propulsion. The solid-fuel motor in the Mk 46 Mod 0 was not successful. The much more numerous Mod 1 (6,608 produced) is driven by a motor fueled by a liquid monopropellant.
A NEARTIP (Near-Term Improvement Program) and Mod 6 refit program began in the early 1980s to counter the loss in acquisition range due to introduction of anechoic hull coatings and to improve shallow-water capability. NEARTIP features an improved sonar transducer and a digital guidance and control system with correlation channel and second gyro; engine improvements included a slower search speed for greater range and lower self-generated noise.
Compared to the Mk 44, the Mk 46 is faster, dives deeper, and has approximately twice the range.
VARIANTS •
Mk 46 Mod 2 (3,344 produced for Foreign Military Sales/FMS
customers) had improved Electronic Counter-Countermeasures (ECCM)
logic.
Mk 46 Mod 4 is used in the Captor mine, which is laid in geographic chokepoints and lies dormant until activated. Operating autonomously, the torpedo’s seeker tracks ship noises and leaves the special capsule when a target is within range.
NEARTIP total of 4,922 kits was procured for the US Navy; refitted torpedoes were designated Mk 46 Mod 6. FMS production totaled 311.
Mk 46 Mod 5 are new-manufacture torpedoes with NEARTIP features that were first authorized for US Navy in the late 1970s as an interim measure (575 produced). As development of the Mk 50 Advanced Lightweight Torpedo (ALWT) hit delays, an additional 4,205 Mk 46 Mod 5 were authorized from FY1983 to FY1987. 1,278 were produced for FMS sales.
DEVELOPMENT •
Aerojet Electra Systems Co. of Azusa, California, developed and produced both the Mod 0 and Mod 1.
The Mk 46 achieved initial operational ca-
pabilityin 1966 for the Mod 0 and 1967for
the Mod 1. Honeywell Defense and Marine Systems of Everett, Washington (which became Alliant Techsystems, Inc., in September 1990), captured the later production contracts, completing the last
Mod 1 in 1971 and the last of 23,000 Mk
46s in the mid-1990s. License production by Mitsubishi in Japan began in 1982.
Alliant also produced the Mk 46 Mod 2, Mod 5, and NEARTIP update kits. The
last US Navy funding was authorized in
FY1987, but FMS continued for almost
another decade.
A list of aircraft and surface-ship classes that do not carry the Mk 46 would be far shorter than the list of those that do.
SPECIFICATIONS •
weight 508 lb (230 kg) warhead 95 lb (43 kg)
DIMENSIONS
length 8 ft 6 in (2.59 m)
diameter 12 3/4 in (324 mm) warhead conventional PBXN-103 high explosive
guidance active/passive acoustic homing; capable of repeated attacks using “snake-search” method
POWERPLANT 5-cylinder cam engine with Otto liquid monopropellant fuel; contra-rotating propellers
SPEED 45 kts; max range 5.9 nm (6.8 mi; 11 km); max depth classified
(greater than 984 ft/300 m) Mk 48 heavyweight torpedo
The Mk 48 is a heavy, wire-guided, long-range, antisubmarine and anti-surface-ship torpedo that succeeded the Mk 37. The Mk 48 is generally considered the most advanced torpedo in Western naval inventories. Still, in the late 1970s advances in Soviet submarine capabilities reduced its margin, leading the Navy to begin the Advanced Capability (ADCAP) program led by Hughes.
The Mk 48 is divided into five component groups. The nose group contains the sonar and homing equipment; next are the warhead, control (with gyro, command, and power units), and fuel tank groups. The fuel tank also holds the command wire dispenser. The afterbody/tail-cone group consists of the engine and steering surfaces. The all-digital Mk 48 Advanced Capability (ADCAP) is virtually a new torpedo, possessing much greater “intelligence,” speed, and range.
Following launch, the submarine performs a wire-clearance maneuver and the torpedo heads to a preselected “enable point.” At the enable point, the acoustic search program guides the torpedo in a programmed search for the target. Once the target is acquired by the torpedo’s sonar, the Mk 48 maneuvers to lock-on and accelerates to intercept.
The ADCAP effort suffered cost growth and delays during the first few
years due in part to Hughes’ inexperience in developing torpedo sensors as well as a continuing, and increasingly pessimistic, reassessment of the Soviet nuclear submarine threat. Each reassessment resulted in demands for more of every parameter.
For example, the Mk 48 Mod 4 interim ADCAP variant entered production at an accelerated rate in 1978 to take advantage of improvements in performance, active and passive acoustic search range, anti-surface-ship capability, and ease of operation studied. The later “Near-Term” Mod 5 ADCAP upgrades existing torpedoes to Mod 4 with a Hughes Aircraft electronically steered, higher-powered active sonar and a larger fuel supply.
Meanwhile, the “Full-Up” ADCAP
continued development, spurred by continuing improvements in Soviet submarines. Further expansion of the operating envelope, higher fuel delivery rates and greater fuel capacity, further improvements in acoustics and electronics, thicker shell, speed increased to more than sixty knots were the result. The Hughes Guidance and Control subsystem has two computers, signal processor, digital-based, electronically steered active sonar, and Inertial Measurement Unit (IMU). It is capable of acoustic homing on fast-moving targets in shallow water and strong thermal gradients. Unfortunately, program delays continued as the Navy and Hughes played catchup while tests to existing versions hit their inevitable snags.
US Navy apprehensions about the growing quality of Soviet submarines persisted right up to the moment of the Soviet Union’s collapse. Almost overnight, that collapse alleviated the urgency of ADCAP development, and production withered.
VARIANTS
• Mk 48 Mod 1 was the product of Gould (formerly Clevite Corp. and later Westinghouse) and Naval Surface Warfare Center at White Oak, Maryland,which began work on this variant in 1967. Propelled by a piston (swashplate) engine with a different acoustic homing system from the Mod 2. Mod 1 entered production in 1972.
Mk 48 Mod 3 was provided with TELECOM (Telecommunications) two-way communications link that transmits 14 torpedo parameters once per second through the wire guidance path Major production variant.
Closed-Cycle Advanced Capability Propulsion System (CCACPS) was a Product Improvement to the ADCAP torpedo with a propulsion system based on the Mk 50′s Stored Chemical Energy Propulsion System (SCEPS). Full-Scale Development (FSD) was planned to start in March 1989 but was delayed several times and eventually canceled.
DEVELOPMENT •
Development began in the early 1960s. The Ex-10 RETORC
(Research Torpedo Configuration) turbine-propelled torpedo was the joint experimental project of Pennsylvania State University Applied Research Laboratory and Westinghouse Electric that began in the early 1960s. This led to the Mk 48 Mod 0/2 turbine-propelled variants; the Mod 2 lost in competition with
Clevite’s Mk 48 Mod 1, with the latter
achieving initial operational capability in 1972. Production versions built by West-inghouse (formerly Gould, Inc.) Naval Systems Division in Cleveland, Ohio, and Hughes Aircraft Company in Forest, Mississippi.
Plans for 320 ADCAP torpedoes per year fell afoul of program problems as well as the diminution of the Soviet submarine threat. Until FY1992, production featured firm-fixed-price competition between Westinghouse and Hughes Aircraft Co.’s Undersea Weapons Division in Buena Park, California.
Beginning in FY1992, the production rate was reduced to minimum sustainable level for just one manufacturer. Hughes emerged the victor of a “winner
take all” competition to produce 324 tor-pedos over a five-year period.
All US submarines (SSN/SSBN) carry the Mk 48 torpedo.
SPECIFICATIONS •
WEIGHT 3,450 lb (1,565 kg) warhead 650 lb (295 kg)
DIMENSIONS
length 19 ft 2 in (5.84 m)
diameter 21 in (533 mm) warhead conventional high explosive
(PBXN-3)
guidance can be launched as free-running or wire-guided free-running; active or passive acoustic search and terminal homing
powerplant 500-hp axial-flow, gas-piston (swashplate) pump-jet using Otto II monopropellant (nitrogen ester and Hydroxylamine Perchlorate/ HAP oxidant) liquid fuel
SpEED 55 kts max; max range at 55 kts, 20 nm (23 mi; 37 km); range at 40 kts, 27 nm (31 mi; 50 km); max depth 2,500 ft (760 m)
Mk 50 lightweight torpedo
The Mk 50, formerly known as the Advanced Lightweight Torpedo (ALWT) , is the successor to the Mk 46 for use by fixed-wing Antisubmarine Warfare (ASW) aircraft, helicopters, and surface ships. The Mk 50 is constrained by the need to stay within the Mk 46′s weight and dimensions as well as having to fit within the length and width of the S-3A Viking’s weapons bay. In addition, the Mk 50 will be carried in the Vertical Launch ASROC antisubmarine rocket launcher. (It was also to have been the conventional payload for the canceled Sea Lance ASW missile.)
Compared to the Mk 46, the Mk 50 isfaster and will dive to a greater maximum depth. Its passive/active seeker can generate multiple, selectable transmit-and-receive beams and home on its target
Mk 50 Advanced Lightweight ASW Torpedo
ALLIANT TECH SYSTEMS
from twice as far away as the Mk 46. The AN/AYK-14 on-board, programmable, digital computer analyzes signal returns in real time and provides mission control, navigation, and target detection and tracking.
The larger warhead was designed by the Naval Surface Warfare Center. The propulsion system is a closed, Rankine-cycle engine that uses a lithium-sulfur hexaflouride reaction to generate steam. The Mk 50 also has better counter-measures resistance and lower radiated noise than the Mk 46.
An earlier version of the ALWT was known as the Barracuda; the current Mk 50 logo shows the fish, but the name is not often used and is not official.
The Mk 50′s size and weight constraints worried many late-1980s Western analysts who regarded the improving Soviet nuclear submarine fleet with increasing trepidation. Despite the real improvements in speed and operating depths, the Mk 50′s warhead seemed too small to threaten the double hulls of Soviet boats. Use of a directed-energy warhead similar to the shaped charge found in antitank missiles would enhance performance, and development was believed to be under way.
VARIANTS •
Mk 51 was the McDonnell Douglas/Raytheon entry in the 1979
“swim-off” with Honeywell/Garrett. (Gould/Hughes, Westinghouse offered a third contestant, but theirs was not selected for the swim-off.) Powered by silver-oxide electric battery (General Electric) and fitted with Raytheon side-looking linear or flank arrays.
DEVELOPMENT •
Development began in August 1975. Alliant Techsystems (formerly Honeywell Underseas Systems Division) in Hopkins, Minnesota, is prime contractor. Westinghouse in Baltimore, Maryland, was selected as second source in May 1987; Martin Marietta supplies the command-and-control system for West-inghouse team.
Alliant and Westinghouse both received initial production contracts, but funding slipped in later years.
The Mk 50 was to replace the Mk 46 in many Western navies, but its cost seems likely to limit foreign sales.
SPECIFICATIONS •
WEIGHT 800 lb (363 kg)
warhead approx 100 lb (45.4 kg) DIMENSIONS
length 9 ft 6 in (29 m)
diameter ]2¥4 m (324 mm) warhead conventional warhead; a directed-energy (shaped-charge) warhead has been considered guidance active and passive acoustic homing with multiple selectable transmit/receive beams; directed by AKY-14 programmable digital computer powerplant Garret Pneumatic Sys-
terns Stored Chemical Energy Propulsion System (SCEPS) using a closed cycle steam turbine driving a pump
jet
speed 50+ kts; max depth more than
1,968 ft (600 m)
