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HMAS Stuart fires an exercise MU90 lightweight torpedo
as part of preparations needed to fire the live 'war shot'
in the EAXA (East Australian Exercise Area), off NSW's
South Coast. Credit: CoA / Brenton Friend
Our venerable but still highly capable RAAF AP-3C
maritime patrol aircraft can drop Mark 46 torpedoes
and fire AGM-84 Harpoon anti-ship missiles.
Because Mark 54 was developed from the Mark 46 it
wouldn’t have required too much work to enable the
Orions to launch Mark 54 torpedoes, but because
operational capability of the Poseidons is not too far
away the RAAF appears to be sticking with the Mark
Is there ever a likelihood in the near future of
settling on just one type of lightweight torpedo for the
ADF? Not as far as APDR can see.
MARK 46 LIGHTWEIGHT TORPEDO
The Mark 46 torpedo is the backbone of the United
States Navy's lightweight anti-submarine warfare
torpedo inventory, and is the current NATO standard.
They are in current use by 35 international defence
These aerial torpedoes are designed to attack
high-performance submarines. From 2014 onwards
they have been replaced by the Mark 54 torpedo
which is a development from, and has a number of
components in common with, the Mark 46.
The Mark 46 torpedo Mod 5 used by the ADF
weighs 235 kg and carries a 44 kg warhead. It has
an operational range of 11 km and can descend
to a depth of 365 metres. It has a two cylinder
reciprocating external combustion engine which uses
Otto fuel II, a mixture of three synthetic substances
which do not need exposure to any oxidant to ignite
and release energy, as its three components will react
among themselves whenever vaporised and heated.
The torpedo’s guidance system is active sonar or it
can be passive/active acoustic homing.
MU90 – FRIGATES AND
A report in Seawaves.com on-line magazine issue
dated 25 March 2017 noted that during the recent
Exercise Ocean Explorer 17, completed mid-March
2017 in the West Australian Exercise Area, HMAS
Melbourne, with the support of Collins class
submarine HMAS Dechaineux, conducted three
successful exercise firings of its MU90 torpedoes.
Staff Officer Force Anti-Submarine Warfare
Lieutenant Commander Chris Straughan from the
Australian Maritime Warfare Centre embarked
in Melbourne for the trial. He said the torpedo
was designed to counter any type of nuclear or
“The MU90 torpedo
provides the Royal Australian Navy with one of the
most capable lightweight torpedoes in the world. It
is designed to detect and attack deep, quiet running
submarines,” he said.
He continued “The Australian Maritime Warfare
Centre conducted the trials to test the performance
of the torpedo against a live submarine. The results
will be used to formulate new tactics, techniques
and procedures. It is part of an ongoing weapons
performance program that has been developed by
the Centre as part of the Fleet Warfighting Strategy.”
Do exercises such as this always go to plan? Not
APDR has a copy of a Hot Issue Brief issued
within the former Defence Materiel Organisation (now
CASG) 18 November 2010 on the subject ‘Loss
Of An MU90 Lightweight Exercise Torpedo In The
Navy's Western Australia Exercise Area’. It states ‘At
7:40 am local time on Thursday 18 November 2010,
a MU90 Lightweight Exercise Torpedo fired from
HMAS WARRAMUNGA was lost. The torpedo ran
for a much shorter than planned period and then shut
down. It was seen on the surface, as it is programmed
to do so it can be recovered, but sank shortly
afterwards in 42m of water. The torpedo is equipped
with an underwater pinger to assist with location
and recovery in case of just such an event. The
MU90 exercise torpedo does not have a warhead
and as such, poses no danger to the public or the
environment. When located, recovery of the torpedo
will be attempted with assistance provided by Navy
clearance divers who are on standby for this task.’
Fortunately workup of the MU90 torpedo has
proceeded more smoothly since then to the stage
where it now has operational capability in the fleet.
The MU90 torpedo is a fire-and-forget weapon
designed to counter any type of nuclear or conventional
submarine, acoustically coated, deploying active or
passive homing. It weighs 304 kg with a range of
up to 25 km and speeds can be set up to 93 km/hr.
Before being launched, its target is set in the
torpedo and once it is in the sea, homing guidance to
the target, usually a submarine or a torpedo fired by
the enemy, is provided by passive or active homing.
What does this mean?
Passive acoustic homing means transducers
placed around the MU90 listen for any sounds being
emitted by its chosen target. For example where the
cavitation and other sounds of a departing submarine
or an approaching enemy torpedo are detected in
three dimensions, the MU90 changes course in the
direction of the loudest underwater noise related
to its set target. Obviously very smart sensors and
computer software are required to make this system
reliable and effective.
What happens if the submarine is totally silent
and passive acoustic homing provides no guidance?
Active homing means the torpedo turns on its sonar
autonomously to detect the location of the target
submarine. If the submarine remains stationary it will
be hit. If it changes track by departing, or if incoming
torpedoes aimed at the MU90 launch warship, are
detected by the sonar, this will cause the MU90 to
correct its own track to the point of interception.
In the 2009 Defence White Paper, the Australian
Government identified anti‐submarine warfare as a
key capability priority for modernising and enhancing
the ADF. As early as 1997 Defence had reached the
conclusion that the Mark 46 torpedo’s limitations
meant a new torpedo needed to be acquired. On
checking what might be available, Defence’s project
team made a major mistake in assuming that it was
4/05/2017 3:08 PM
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