ComNavOps has called for the
design and construction of a dedicated anti-submarine warfare (ASW) ship
instead of a frigate. The reason for
this is that our current ASW vessel is the Burke class destroyer which costs
$2B each, conservatively, and is far too expensive to risk playing tag with
submarines, especially small, silent, non-nuclear shallow water subs. Further, the Burkes are primarily anti-air
warfare (AAW) vessels and do not train for ASW enough to be effective at
it. That leads to the situation of a
poorly trained and very expensive ship being asked to conduct ASW against an
enemy that possesses most of the inherent advantages to begin with. We need an ASW vessel that is dedicated to
ASW so that the ship and crew will be thoroughly trained and cheap enough to be
expendable when playing tag with submarines.
However, in order to be
effective, an ASW ship must have effective weapons. Currently, for close range encounters, the US
Navy has only the standard Mk32 triple torpedo tube system (12.75”, 324mm)
which launches lightweight Mk 46, Mk 50, and Mk 54 torpedoes. Unfortunately, these torpedoes have problems
with their shallow water performance.
The Mk 54, in fact, was developed in response to an urgent operational
need resulting from shallow water performance problems demonstrated by the Mk
50. The Mk 54 has had its share of
problems with DOT&E assessing it as “not operationally effective” in its
2014 Annual Report and states in the 2016 Annual Report that the Mk 54 “will
remain not effective even with the Mod 1 fixes”.
The US Navy also has the
vertical launch ASROC system but it is not a close range system. It has a maximum range of 15 miles. The minimum range is unknown but given that
the weapon is a homing torpedo, it figures to be substantial.
Thus, the Navy’s only
shipboard, close range ASW weapons are torpedoes which have faulty shallow
water performance, are subject to minimum engagement limits, and are assessed
as “not effective”.
As subs have grown quieter
and more advanced around the world, and as US Navy ASW proficiency has
atrophied, the likelihood that we will have more late detection, close range, unexpected
encounters has increased. Further,
shallow water ASW with its attendant noisy (poor sonar) conditions almost
guarantees much closer detections. We
need a quick reaction, anti-submarine weapon for those surprise, close range
encounters. The Navy has had such
weapons in the past but abandoned them with the advent of the ASW helicopter
which was supposed to keep the ship at arm’s length from the submarine. In deep water, this is a reasonably valid
concept but not in shallow water which is likely to be the more common ASW
arena in the future.
Close range ASW weapons of
the past include the iconic depth charge of WWII and the Hedgehog which was a
mortar system that launched contact fused charges a few hundred feet in front
of the ship. These weapons were
eventually abandoned in favor of helicopters and homing torpedoes.
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| WWII Era Hedgehog |
Today’s version of the
Hedgehog was developed by the Soviet Navy and is called the RBU. The RBU is a short range rocket launcher
which fires high explosive charges with either contact or depth fusing. The charges can be fired singly or in
salvo. The launcher comes in various
sizes which differ in the number of launching barrels, typically 6-12. Maximum range is 1000 yds – 6500 yds,
depending on the version. The launcher
is moveable in train and elevation and is rapidly and automatically reloadable
from an integrated hatch at the base.
Magazine capacity is up to around 100 reloads, depending on version. RBU’s were standard on all Soviet warships.
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| Russian RBU-1000 |
The RBU offers the
capability of instantaneous attacks against very close contacts. The charges are immune to countermeasures
and, in contact fuse mode, offer positive feedback on hits. The “dumb” nature of the free-sinking charges
ensures that they offer no threat to the launching ship unlike homing torpedoes
which can target the launching ship. To
prevent self-targeting, torpedoes have minimum safe distance arming
limits. Unfortunately, the minimum
arming distance precludes engagement within that range. Thus, the Navy’s short range torpedo is not
really short range or, rather, short range is a relative term. I’ve been unable to find a citation for the
minimum safe arming distance for US torpedoes.
Thus, an RBU can fill the gap between the minimum arming range of the
torpedo and the ship.
An upgraded version of the
RBU, the RPK-8, uses the RBU launcher with a 90R homing head charge which
offers increased chance of a hit. The
homing search radius is 130 m and the effective range is 600-4300 m and
effective depth is 1000 m (1). Again,
this demonstrates the drawback to homing capabilities in the form of minimum
safe distance limits from the launch ship.
Still, this may represent a balance of close range and enhanced kill
probability via homing. The system is
quick reaction with a combat ready time of 15 sec (1).
RBU rocket charges are also
much cheaper and smaller than torpedoes which allows many more to be carried
and used. In combat, when many questionable
contacts will be prosecuted (no Captain will risk not prosecuting a
questionable contact that could turn out to be real), the ability to use cheap,
plentiful charges rather than scarce, expensive torpedoes could be a welcome
option.
![]() |
| Russian Parchim Class Corvette Firing RBU-6000 |
Surface ships engaged in
shallow water ASW or merely operating in shallow water will likely find
themselves in surprise, close range encounters with non-nuclear submarines and
a short range, quick reaction ASW weapon could provide the defense needed to
survive the encounter. The small size
and weight of the launcher makes it suitable for any ship and allows it to be
added almost anywhere that a small deck penetration for the reloads can be accommodated.
The US Navy should give
serious consideration to developing or obtaining such a weapon system. The combination of a small, dedicated, cheap
ASW vessel and basic, reliable ASW weapons such as an RBU-Hedgehog along with
lightweight torpedoes and various sonar sensors would provide the Navy with a
viable, effective, and expendable ASW vessel well suited for shallow water
operations.
On a side note, a time-fused
version could possibly be adapted to torpedo defense by launching a salvo timed
to drop in front of an incoming torpedo and explode – the anti-torpedo
equivalent of CIWS.
Note: Russia offers the RPK-8 as an export weapon system – no
development needed and it would be satisfying to “take” something from the
Russians for a change!
Note: This is not a replacement for anti-submarine
torpedoes. It is a complement intended
to provide effective attacks in close range, surprise encounters.
_____________________________________
(1)Russian Defense Export
website, products/naval systems/shipborne weapons/RPK-8,


