The Modern Hedgehog
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.
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| 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
Note: This is not a replacement for anti-submarine torpedoes. It is a complement intended to provide effective attacks in close range, surprise encounters.
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(1)Russian Defense Export website, products/naval systems/shipborne weapons/RPK-8,
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