Type
Air/ship/missile-launched, solid propellant
or liquid-propelled, homing torpedo.
Development
Development of the Mk 46
torpedo, by Aerojet Electro Systems, began
in 1958 following a 1956 feasibility study.
An Operational Requirement was issued
in 1960, when the need to replace the Mk 44
became fully apparent. The Mk 44 had not
long been in service, but the threat posed
to US battle groups by a new generation of
deeper-diving, faster and quieter former
Soviet Union submarines made it imperative
that a more capable counter weapon be
developed. Production of the Mk 46 Mod 0
began in 1963 and, although early production
models were delivered to the USN in 1965,
the official deployment date was 1966.
Maintenance difficulties with the original
Mod 0 led to the lighter, liquid-powered Mod
1 and Mod 2 versions.
Development of the follow-on Mod 1 began in
1964, the first production versions were
tested in 1966 and Mk 46 Mod 1 was
introduced into service in 1967. One
of the improvements to the Mod 1 was to
replace the original solid-fuel turbine
engine used in the Mod 0 with a two-stroke
swash-plate engine driven by a new
high-energy mono-propellant, known as Otto
fuel after its inventor. Further improvement
programmes produced the Mod 2, which became
available in quantity in 1971, with upgrades
including improved computer logic and a new
autopilot, to permit re-attack. The Mk 46
Mod 2 was also tailored to interface with a
new Helicopter Attack Tactical System (HATS),
in which the search mode could be selected
by the helicopter's fire-control system. All
remaining Mod 0 torpedoes were converted to
Mod 2 standard by 1975.
A Phase Two
Mod 1 programme was introduced to give the
Mod 1 a better shallow water performance,
and improved resistance to countermeasures.
These modifications incorporated most
of the Mod 2 improvements, with the
exception of HATS mode. A proposed Phase
Three would have allowed launch at shallower
depths and enabled the torpedo to run at
greater depths, but such improvements could
ultimately only be accommodated in a
radically new weapon, the Mk 50 Barracuda
(for details see separate entry). Further
improvements to the control system,
designated Mod 3, were cancelled, while Mod
4 was a variant tailored to the requirements
of the Mk 60 Captor (encapsulated torpedo)
anti-submarine mine (for details see
separate entry). This version was later
improved and became the Mk 46 Mod 6 but was
then cancelled in 1990.
In 1972, to
bridge the gap until the Mk 50 became
available in large numbers, the USN
initiated the Mod 5 Near Term Improvement
Programme (NearTIP). What finally
emerged was virtually a new torpedo produced
by Honeywell Defense Systems (now Raytheon
Defense Systems) with an improved seeker,
digital computer and a new two-speed motor
to extend range. The Mk 46 Mod 5, which
entered service in 1984, was also designed
for, and is capable of combating the
adoption of anechoic coatings by Russian
submarines (codename Clusterguard). In
addition to new-build weapons, all Mod 1s
were upgraded to Mod 5 standard.
The US Navy
introduced the first of two shallow water
modifications in 1984, designated Mod 5A(S).
These were to improve performance
against slow submarines at periscope depth
in both deep and shallow water. Normally
such targets are difficult to engage because
they provide little Doppler shift (which is
what the torpedo seeker uses to distinguish
target from background noise). The second
shallow water modification was developed by
Honeywell to give the torpedo an alternative
anti-surface ship mode so that, for example,
torpedo-carrying missiles like ASROC can be
employed against surface targets. This
version was designated Mod 7, but was
cancelled following an unsuccessful
operational evaluation.
In 1996 a Mk
46 Service Life Extension Programme (SLEP)
was proposed to incorporate some shallow
water performance improvements, and further
modernise these torpedoes. This
modification was designated Mod 5A(SW),
adding a bottom avoidance capability and
improved shallow water running.
The
air-launched version of the Mk 46 has been
cleared for carriage on a wide range of
fixed- and rotary-wing aircraft including
the AB 212 ASW, AS 532 Super Puma, EH 101,
H-76 Eagle, S-70B Seahawk, SH-2G Super
Seasprite, SH-3 Sea King, Westland Sea King
helicopters and A-4 Skyhawk, A-6 Intruder,
A-7 Corsair, Atlantique 2, CASA-212
Patrullero, CN-235MPA, Fokker 50, and P-3
Orion aircraft.
In 1993, the USN authorised a
feasibility study to examine merging the Mk
46 and Mk 50 torpedo technologies to provide
a low-cost weapon for use in littoral
waters. The result of this study was
the decision to retain the Mk 46 Mod 5A(S)
and Mod 5(SW) versions, the Mk 50 and to
introduce the Mk 54 LHT.
A report in
1998 indicated that modified Mk 46 torpedoes
were being used as remote underwater
sensors. For further details see
Unclassified Projects.
In 1999, a Mk
46 torpedo was tested as part of the DARPA
undersea littoral warfare programme, with
the torpedo linked to a surface buoy via a
fibre optic cable, so that acoustic data
could be transmitted back from the torpedo
seeker. The fibre optic cable could
also be used to control the torpedo.
Description
The Mk 46 is a
deep-diving, high-speed torpedo of modular
design intended mainly for use against
submarines. It can be launched from
helicopters and fixed-wing aircraft as well
as from surface ships. The torpedo consists
of four subsystems which are independently
replaceable and interchangeable without
alteration to the overall performance or
functional characteristics.
Current Mk 46
Mod 5 torpedo is 2.6 m long, has a body
diameter of 320 mm and weighs 231 kg.
The warhead used is a Mk 103 Mod 1 which
contains 44 kg of high explosive, which is
activated by a proximity fuze as well as an
impact fuze designed to detonate even if the
torpedo strikes the target at a shallow
angle.
Little
information has been released on the
guidance system except the Mod 5 features a
new passive/active sonar system capable of
detecting most types of underwater submarine
targets including anechoically coated hulls.
The sonar offers improved target
acquisition capabilities in all types of
acoustic environment, including shallow
water. The guidance and control systems have
also been upgraded and now feature re-attack
logic.
The Mk 46 Mod
0 used a solid fuel motor whereas the Mod 1,
which is slightly lighter, uses a
five-cylinder liquid-mono-propellant (Otto)
motor. This later propulsion system
was introduced because of the maintenance
problem with the original solid fuel motor,
and is also employed in the two-speed Mod 5
version. The slower second speed was
introduced to increase the torpedo's
endurance by some 30 to 50 per cent. However,
once the torpedo has locked on to its target
the torpedo still attacks at the same high
speed of around 45 kt provided by the
original Mk 46.
On release,
after entering the water and discarding its
retarding parachute, the Mk 46 torpedo
starts a helical search pattern, acquires
the target at a reported maximum range of
600 m and attacks; if it misses the target
it is capable of multiple re-attacks.
The Mk 46 is reported to have a maximum
range of around 11 km at a depth of 15 m,
decreasing to 5.5 km at a depth of 455 m.
Operational
status
Mk 46 Mod 0 torpedoes,
which were only produced in limited numbers,
entered service in 1963. The Mod 1
version entered service in 1967 and the Mod
2 in 1971. By early 1975, most of the US
Navy Mod 1 torpedoes had been converted to
Mod 2 standard by modification action.
NEARTIP implementation was applied to US
stocks in the form of modification kits
applied on a retrofit basis in the early
1980s, but the first NEARTIP Mod 5 torpedoes
entered service in 1984. The improved Mod
5A(S) entered service in 1990.
Since 1965
more than 25,000 Mk 46 torpedoes have been
produced for the USN and other navies.
Users of the Mk 46 torpedoes include:
Australia, Belgium, Brazil, Canada, Chile,
China, Egypt, France, Greece, Indonesia,
Iran, Israel, Italy, Japan, South Korea,
Morocco, Netherlands, New Zealand, Norway,
Pakistan, Peru, Poland, Portugal, Saudi
Arabia, Spain, Taiwan, Thailand, Turkey and
UK.
The Mk 46 Mod
5 torpedo is also used as the payload for
the USN's RUR-5 ASROC (Anti-Submarine ROCket)
ASW weapon and is one of the payload options
for the RUM-139 VL-ASROC. Mk 46
torpedoes have been fitted to the initial
in-service RUM-139, but may be replaced by
Mk 50 Barracuda torpedoes in the future. It
was reported in 1996 that 1,000 Mk 46 Mod 5
torpedoes would be modified to the SLEP
standard for the US Navy. These will be
designated Mk 46 Mod 5A(SW) and will be
introduced in a series of upgrades to
maintain stocks in service until 2017. The
first Mod 5A(SW) standard torpedoes entered
USN service in late 1996. A further 4,000 Mk
46 torpedoes will be stored or used for
spares. The Mk 54 Lightweight Hybrid Torpedo
(LHT) programme (see separate entry) will
upgrade some further Mk 46 torpedoes with Mk
50 torpedo assemblies. A contract was also
placed by the Canadian Navy to upgrade its
Mk 46 Mod 1 torpedoes.
It is
reported that Raytheon is continuing to
offer surplus Mk 46 stocks and upgrade kits
(based on the US Navy's SLEP programme) to
international customers. In 1998
Raytheon was contracted through US Foreign
Military Sales channels to supply Mk 46 Mod
5 weapons to Saudi Arabia, Egypt and one
other unnamed navy. The deal with Egypt also
includes the upgrade of 20 Mk 46 Mod 2
rounds to Mod 5 standard. In November 1998
it was reported that the Taiwan's Republic
of China Navy (RoCN) had requested the
purchase of 131 Mk 46 Mod 5A(S) torpedoes.
The torpedoes requested are air-dropped
versions for deployment on the ten S-70C (M)
Thunderhawk anti-submarine helicopters
operated by the RoCN from its Cheng Kung
class (Perry type) and Kang Ting
class (La Fayette type) frigates.
Specifications
Length:
2.6 m
Body diameter: 320 mm
Launch weight: 231 kg
Warhead: 44 kg HE
Guidance: Active/passive sonar homing
Propulsion: Thermal chemical engine
Range: 5.5 to 11 km depending on
depth
Speed: 45 kt
Contractors
Raytheon
Defense Systems, Mukilteo, Washington.
Aerojet Electro Systems, Azusa, California (development
and early production of Mod 0 and 1).
