Why Do We Have Lightweight Torpedoes?

During the Cold War, the US Navy concluded that lightweight torpedoes were largely ineffective against Soviet submarines, in terms of achieving a kill.  Even heavyweight torpedoes were questionable and thought to require multiple hits to kill.  Lightweight torpedoes were considered more of an annoyance to Soviet subs than a lethal threat.
 
Lightweight torpedoes are a lethal threat only to small, lighter built diesel subs.
 
Lightweight torpedoes are not a ship-sinking threat to anything much bigger than a patrol boat and are not capable of sinking surface ships, either merchant or naval.
 
That being the case, why is the Mk54 lightweight torpedo so ubiquitous throughout the surface Navy?  Wouldn’t it make more sense for ships to mount heavyweight torpedoes?
 
Here’s a brief comparison of the Mk48 heavyweight and Mk54 lightweight torpedo characteristics.  Characteristics vary, of course, depending on the exact model but these are representative.  Note the lightweight torpedo’s warhead weight and range deficiencies compared to the heavyweight torpedo.

The Mk48 heavyweight torpedo can do anything the lightweight can (which isn’t much) plus it is capable of : 

• Sinking merchant ships
• Sinking submarines
• Sinking surface ships
• Destroying maritime structures (oil platforms and such)

 
There have been reports over the years that the Mk48 has problems in shallow water.  The lightweight torpedo was intended, in part, to be the answer to shallow water issues but has had its own reported problems.  The last DOT&E annual report that I can find for the Mk54 assessed it as operationally ineffective (2014 report) and not operationally suitable (2023 report).
 
All of this leads me to ask, why isn’t the Mk48 standard on surface ships?

Surface Ship Torpedoes

In a previous post, we touched on the subject of anti-surface torpedo tubes in surface ships.  Yes, many ships today have torpedo tubes but the majority are intended for anti-submarine use and utilize lightweight torpedoes.  The US Navy’s standard surface ship torpedo armament is the Mk32 triple tube launcher with Mk46/50/54 lightweight anti-submarine torpedoes.  These torpedoes may or may not have an anti-surface ship mode but they are not ship killers.  The ship killing torpedo in the US Navy is the Mk48 ADCAP (Advanced CAPability) heavy torpedo and even this is intended primarily as an anti-submarine weapon.

                 Mk 48        Mk54         Mk50         Mk46

Range, yds       35000        ?            16000        12000

Speed, kts       55 (63?)     40+          50+          45

Diameter, in/mm  21/533       12.75/324    12.75/324    12.75/324

Length           29’2”        8’11”        9’6”         8’6”

Weight, lbs      3450         608          800          508

Warhead, lbs     650          95           100          95

Cost             $2.4M(FY88)  $0.8M(FY14)  $1M(FY02)

For comparison, here are a couple of the main Russian Torpedoes.

                 Type 65      Type 53 UGST (2)

Range, miles     62@35mph     25

Speed, kts       50           26-45

Diameter, in/mm  25.6/650     21/533 

Length           30           24’  

Weight, lbs      10450        3800   

Warhead, lbs     990-1225     801                 

The Mk46 was designed for open ocean, deep water anti-submarine use and had problems in shallow water.  The Mk50 was developed as the replacement for the Mk46 but encountered problems.  The Mk54 was developed to rectify the problems identified in the Mk50 but does, itself, suffer from shortcomings against shallow water non-nuclear submarines.  A Mk54 Block Upgrade (BUG) program was initiated to address the problems but DOT&E still assessed the torpedo as not operationally effective in its intended role in a 2014 Annual Report and reiterated that assessment in the 2016 Annual Report despite additional upgrade efforts.

According to Polmar (1), US surface ships had anti-ship torpedo tubes until the late 1950’s.  During the 1960’s the Mk48 was intended to be fitted to surface ships for long range, wire guided ASW use but that never occurred.

Polmar also notes that a dedicated anti-surface torpedo was proposed by the Navy in the mid-1980’s (1).  The torpedo was envisioned as a low cost ($200K in then year dollars vs. $2.43M per Mk48 in FY88), no frills alternative to the Mk48.  The program was cancelled in the late 1980’s.

As a brief historical reminder of the use of anti-surface torpedoes on surface ships, here’s a list of the post-WWII ships that have had large, anti-surface-capable torpedo tubes installed.

• Garcia/Brooke Class FFG 2x 21” fixed, stern tubes, Mk37 Torpedo
• Sherman Class DD 4x 21” tubes
• Mitscher Class DL 4x 21” tubes
• Gearing Class DD 10x 21” tubes, twin trainable quintuple mounts, Mk15 Torpedo

That brings us to today.  The US Navy has no surface anti-ship torpedo capability and only a marginally effective submarine launched anti-ship torpedo, the Mk48.

The next question, and the main point of this post, is, does the US Navy need a surface anti-ship torpedo launch capability?

To better frame the question, consider that currently the Burke class DDG probably cannot sink a large ship such as a tanker or large cargo vessel.  If the US attempted a blockade and wanted to sink enemy merchant shipping, the Navy’s surface ships would be hard pressed to accomplish the task.  Small 5” guns are incapable of sinking a ship bigger than a patrol boat and Harpoon or Standard missiles in anti-ship mode will only damage superstructure, not sink a sizable ship.  Smaller ships such as the LCS which would be expected to perform most of the blockade and merchant shipping attacks have zero ability to sink a large ship.  A heavy weight anti-ship torpedo would go a long way toward providing a credible anti-ship capability.

Thus, the main argument for a surface anti-ship torpedo capability is lethality.  Compare the warhead weight of the Mk48 (650 lbs) versus the Kongsberg Naval Strike Missile (276 lbs) which is, apparently, going to be the Navy’s standard anti-ship weapon for smaller ships.  The difference is significant and, while simply comparing warhead weights is fraught with irrelevance, it nonetheless gives some idea of explosive power and concomitant lethality.  Clearly, a heavy torpedo packs a much more potent explosive punch.  Add to that the fact that torpedoes explode on or under the hull and let water in while missiles let air in, and the lethality of torpedoes is accentuated.  Smaller ships such as the LCS would gain a huge increase in lethality by mounting heavy anti-ship torpedoes.

The Mk48 warhead is lighter than the Long Range Anti-Ship Missile (LRASM) (1000 lbs) which may become a standard anti- ship missile for larger ships.  Again, though, the underwater location and nature of a torpedo explosion magnifies its explosive effectiveness.  Thus, even a Burke equipped with the LRASM could benefit from a heavy anti-ship torpedo.  We should also note that the vertical launch version of the LRASM may or may not ever happen and, if it does happen, takes away VLS cells from the ship’s main purpose which is anti-air warfare.

Another argument for torpedoes is their inherent survivability.  Currently, there are no effective active countermeasures to destroy attacking torpedoes and it is debatable how effective acoustic decoys, such as the US Nixie, will be given the Russian development of wake-homing torpedoes.  Unlike anti-ship missiles which are susceptible to electronic countermeasures (ECM), decoys, anti-air missiles, and close-in weapon systems and, therefore, need to be launched in large numbers to ensure sufficient hits, torpedoes can be used in relatively smaller numbers since they are largely immune to countermeasures.

On the other hand, one of the drawbacks to anti-ship torpedoes in the past has been the limited range, at least compared to anti-ship missiles.  The standard WWII Mk15 torpedo, for example, had a maximum range of around 8 miles.  That kind of range is unsuitable for today’s long range, over the horizon type of warfare where anti-ship strike ranges need to be 20-100+ miles.  However, modern torpedoes have greatly increased ranges that bring them in to the low end of anti-ship missile ranges.  For example, while the actual range of the Mk48 is unknown, the often cited range is around 20 miles.  The Mk48 upgrades have increased the fuel load and improved the propulsion so it is reasonable to assume that the range has significantly increased.  30 miles?  60 miles?  Who knows?  The point is that the torpedoes’ range is beginning to approach, for example, the Harpoon range of 60 miles. 

Certainly, modern torpedoes outrange the ship’s onboard sensors which makes them effective to the limit of the ship’s sensors.

Speed is another drawback.  Torpedoes are very slow compared to anti-ship missiles.  A fast torpedo has a speed of 50-60 kts versus even slow anti-ship missiles which have high subsonic speeds.  Thus, the travel time from the launching ship to the target allows for a great deal of movement by the target which complicates the targeting probability of success.  Further, the long travel time allows the enemy the opportunity to strike the launch platform before the torpedoes arrive.  Even if the torpedoes arrive and sink their targets, the launching ships may be destroyed in the interim!

Some of the arguments against torpedoes are valid due to the limitations of US torpedoes whose design and development has languished for decades compared to the advances in Russian torpedoes.  If the US were to develop a completely new anti-ship torpedo, many of the limitations would be eliminated or reduced.

Consider these improvements to torpedo performance.

Range.  Range could be 60-90 miles, matching the low to mid range for anti-ship missiles.  The old Russian Type 65-76 had a range of 60+ miles at 35 mph (2).  The German Navy’s current DM2A4 Seehecht (export designation "SeaHake mod 4") has a reported range of 87 miles (2) with GPS waypoint capability and carries a warhead of 572 lbs.

Speed.  Speed could be 60+ kts.  Russia’s VA-111 Shkval is the extreme example of high speed, reportedly capable of 200+ kts via supercavitation although the high speed comes at the cost of a reduced range of about 9 miles.  The US Mk48 is capable of around 60 kts.

Guidance.  Currently, the US has no wake homing torpedo but there is no technical reason why we could easily develop one.  Thus, a new torpedo could use multiple modes of guidance including passive and active acoustic, wake homing, and GPS/Inertial.  Wire guidance is probably not feasible for a surface ship due to the ship’s maneuvering and near surface turbulence but it’s worth looking at.

WWII Destroyer Torpedo Tubes - Time To Return To The Past?

A modern, new design, anti-ship torpedo could offer a lethality option for surface ships that is currently lacking.  Heavy torpedoes would not negatively impact VLS inventories although deck space and/or internal volume would have to be allocated.  Such a weapon would offer a relatively low cost increase in tactical options to the ship commander and ought to be part of every surface ship’s standard armament.

__________________________________

(1)“The Naval Institute Guide To The Ships And Aircraft Of The U.S. Fleet”, 16^th ed., Norman Polmar, Naval Institute Press, 1997, p.465-469

(2)Submarine Matters blog, 1-July-2015,

http://gentleseas.blogspot.com/2015/07/russian-torpedos.html

Mk54 Torpedo and UONS

In Mar 2010, Fifth Fleet issued an Urgent Operational Need Statement (UONS) to address an emerging submarine threat.  I’ve never found an actual detailed description of the threat but given the Fifth Fleet’s area of operation, the Mid East, the threat is presumably diesel-electric submarines operating in shallow water.  The Navy’s standard anti-submarine torpedo, the Mk48 is not shallow water capable and the smaller Mk54 torpedoes were, apparently, inadequate.  The Mk54 lightweight torpedo Block Upgrade (BUG) was the Navy’s answer to the threat.

The Mk54 has been in production since 2004.  The BUG program began testing in 2011 and continues today with persistent problems.  The program’s focus has been software development, presumably to allow better interpretation of shallow water sonar performance.  The sonar seeker is also being replaced, again, presumably, to allow better shallow water performance.

DOT&E (1) has been quite critical of the Navy’s test program, citing unrealistic target surrogates among other problems.  On the plus side, the test program has uncovered numerous documentation, maintenance, and training issues which have been present since the torpedo’s introduction and which prevent operators from achieving full benefit of the weapon system’s capabilities.  As DOT&E notes in the 2013 report,

“In preparation for the May 2013 test, Navy operational testers uncovered inconsistencies in tactical guidance, documentation, and training for the employment of the Mk 54 BU torpedo, some of which date from the introduction of the Mk 54 Mod 0 to the fleet in 2004. These problems could prevent fleet operators from effectively presetting and employing the Mk 54 BU.”

Further,

“Testing also discovered some required weapon presets were not selectable by crews using the MH-60R combat control system introduced to the fleet in 2010. The Navy’s early fielding and Quick Reaction Assessment processes did not identify these critical shortfalls. The Navy investigated and found it had a problem in communication between the torpedo developers, platform fire control system developers, tactics developers, the training community, and the fleet users.”

Note that the Navy’s test processes failed to identify critical problems.  This is why the independent DOT&E group is so vital.  The Navy has insufficient technical competence to even spot obvious and critical problems.



Mk54 - Urgently Needed



DOT&E’s 2013 assessment included this,

“Almost two years after the early fielding, the Navy has not yet provided fleet operators and trainers adequate employment guidance or completed required operational testing.”

Two years!  And this is for an URGENT Operational Needs request.  Thank goodness it wasn’t a normal request or they’d still be in the paper study phase.

The 2011 DOT&E report has this to say about the Navy’s test protocols,

“To date, the Navy’s emerging threat test scenario execution was structured and attacking crews had perfect knowledge of the target’s location. Also, the Navy conducted testing in a relatively benign area where torpedo interactions with the bottom or false contacts were minimized.”

DOT&E also notes that there are leftover problems with terminal homing, among others, from the Initial Operation Testing & Evaluation (IOT&E) when the Mk54 entered service.

As part of the test program, the Navy has developed a Steel Diesel Electric submarine surrogate target.  Unfortunately, the surrogate does not have the characteristics of the actual threat and is used as a static target – hardly realistic.  Even today, going on four years after the UONS, DOT&E notes,

“The Navy continues to investigate possible surrogates; however, the proposals are unfunded.”

We have an urgent need and nearly four years later we still don’t have a realistic threat surrogate target or even a plan to obtain one.  Who’s responsible for this?

As of 2012, DOT&E reported that,

“… based on completed testing, crews employing the Mk 54 have a limited capability against the UONS threat under favorable targeting and environmental conditions. DOT&E also reported that the Navy’s testing was completed under best-case scenarios, and the Navy did not have an adequate threat surrogate for the UONS threat.”

DOT&E summarized the 2012 testing with these comments,

“Three weapons were fired by an Arleigh Burke class destroyer and five were dropped by MH-60R helicopters. Another five weapons were intended to be dropped by P-3C aircraft, but those events were cancelled due to aircraft material problems. After the testing, the Navy declared the MH-60R runs invalid due to testing irregularities.”

“The Navy conducted the second phase of BUG operational testing off Cape Cod, Massachusetts, in August 2012. The P-8A aircraft delivered eight weapons; MH-60R helicopters dropped another six weapons. Three more planned torpedo runs were not completed.”

Seriously?  Who’s supervising this testing – Wile E. Coyote?  Is this a Road Runner cartoon?  While there are unknowns associated with any test that may cause problems, this level of failure to even complete the tests is gross incompetence.

DOT&E also threw out this gem,

“The time constraints associated with Mk 54 exercise torpedo employment and recovery often do not allow sufficient time for fully operationally realistic events.”

I have no idea what time constraints they’re referring to but given that this is a UONS program, I would think that whatever time is needed is should be allocated.

This is a common theme among the blog posts, isn’t it?  The lack of realistic testing, in particular realistic threat surrogates, for all programs, is putting the fleet at risk by fielding equipment that is needlessly flawed.  This is a consistent shortcoming by the Navy, spanning decades.  All systems will have flaws that can only be uncovered through combat but the tragic part of this is that many of the flaws can be uncovered simply with more realistic testing so that we don’t have to find them the hard way and pay for the knowledge in blood.

(1) Director, Operational Testing & Evaluation, Annual Report, 2011, 2012, 2013