Surface Anti-Submarine Warfare Weapons- Stand-Off Weapons- 2 of 2

The need for standoff weapons for surface ASW is largely tied to improvements in sensors and detection ranges against enemy subs.

Most of our very brief mention of sonar has  been focused on the classic-hull mounted active “pinging” sonar. Familiar to everyone who’s ever seen a submarine, the sonar sends a pulse of sound into the water, and  patiently waits for a return echo.

We’ll save the details of sonar development for a later series of posts, but for now, suffice to say that deep diving submarines can dip under a rapid change in the temperature of seas, known as a thermocline. That rapid temperature shift changes the density of water, and tends to reflect active sonar waves, effectively shielding a submarine from active sonar at medium and long ranges.

The first response to this was Variable Depth Sonar, in which a second active sonar transducer was lowered from the fantail of an escort to a depth below the thermocline. Quite often, this thermocline had the effect of channeling the “ping” of the active sonar to effective ranges beyond what any surface sonar could provide. To effectively target contacts at that range would require even more range than the 5 or so miles the original RUR-5 ASROC could provide.

About that time, gas turbine engine technology was beginning to catch on in helicopters. And remote control of drones was being seen as a mature technology. Coincidentally, the huge numbers of Sumner/Gearing class World War II destroyers were slated to be modernized to extend their service lives, and to upgrade their ASW capabilities from their obsolete WWII fit to cope with their new mission of protecting carrier battle groups from fast, deep diving Soviet subs. And so DASH was born- Drone Anti-Submarine Helicopter.

The QH-50C was a coaxial rotor unmanned helicopter that would fly under radar control to the range and bearing of a sonar contact, and drop one or two Mk 44 torpedoes.

http://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/QH-50C_DD-692_1969.jpg/800px-QH-50C_DD-692_1969.jpg

QH-50C DASH. The winch and reel for the associated Variable Depth Sonar can be seen on the ship’s fantail.

It was less than a rousing success. The aircraft was unmanned, and so lacked much of the redundancy that any manned aircraft would have. But for a ship’s Captain to lose an fairly expensive asset like a DASH looked bad, so many were reluctant to operate them very much. Nor, at the extended ranges of sonar contacts, was the location of the target precise enough to ensure the torpedo had a reasonable expectation of acquiring its target.

While DASH wasn’t a rousing success as an anti-submarine weapon, it did show that operating helicopters from smaller ships was quite possible. As an aside, modified QH-50s equipped with television cameras did admirable work as naval gunfire spotters on the gun line off the coast of North Vietnam. All the accuracy of a spotter, with no worries of a POW if it was shot down.

The second major sonar technology that came to prominence was the passive towed array. Rather than blasting sound energy into the water and waiting for a return, a passive array is a series of hydrophones in the water that simply listen for the distinctive sounds of a submarine.  By towing them at a distance from the escort, most of the ship’s self-noise could be avoided. Advances in signal processing in the 1960s and 1970s made the passive towed array a viable method of detecting enemy submarines at quite long ranges.  Detection at ranges of 50 or even 100 miles were possible.

The problem was, detection was all that was possible. Only the  most general range and bearing information could be derived at extended ranges by a towed array sonar. The challenge was to localize, identify, track, attack and destroy said contact.

The Navy, having learned that small ships could operate helicopters, and with a large number of escorts modified to carry DASH, decided that the best way to prosecute a distant contact would be a manned helicopter. The Sumner/Gearing destroyers of World War II were too small for manned helicopters, but the Brooke/Garcia/Knox classes of escorts could be modified to carry a single mid-sized helicopter. The Navy modified its standard shipboard utitlity helicopter, the Kaman UH-2A SeaSprite. Adding a radar, sonobouy dispenser, a tactical navigation system, and a datalink resulted in the SH-2F.

The Seasprite wasn’t simply a helicopter that happened to be based on an escort. Instead, because of the datalink, it was an extension of the combat system of its parent ship. The sonobouys of the Seasprite would transmit their signals to the helicopter, which in turn retransmitted them to the ship, when an acoustical processor analyzed the signals. Installing a powerful enough computer on board the helicopter simply wasn’t practical. And the deeper diving, faster, quieter submarines meant that unprocessed sonobouy data was unlikely to be sufficient to prosecute the contact.  The processed signals were then transmitted back to the helicopter, where its AN/ASN-123 TACNAV system helped the helicopter localize the submerged contact.  Once the locale of the contact had been roughly determined, repeated passes with a towed Magnetic Anomaly Detector would precisely locate the sub, and a torpedo attack made.

The SH-2F was also equipped with an LN-66 surface search radar (which was not datalinked to the parent ship). This allowed the Seasprite to also provide Over The Horizon Targeting (OTH-T) and supported Anti-Ship Missile Defense (ASMD). The radar wasn’t really intended to pick up incoming cruise missiles. But early Soviet cruise missile subs had to surface to launch their missiles, making them vulnerable to radar detection.

Because it supported multiple missions, the SH-2F and its associated equipment shipboard was known as the Light Airborne Multi-Purpose System, or LAMPS.

Almost immediately after its introduction, the success of the program prompted calls for a more capable platform and associated combat systems.  The Seasprite was a relatively small helicopter, and at a range of 50nm from its ship, only had about an hour to prosecute a contact. The Seasprite soon came to be known as LAMPS I.

The existing ships of the fleet were mostly too small to accommodate any larger helicopters, but the new Spruance class destroyers, and the Oliver Hazzard Perry class frigates could be modified to carry a significantly larger helicopter. Even better, they could be built with hangar space for two helicopters. Larger helicopters would allow more equipment (and torpedoes) to be carried, and allow more time on station to prosecute contacts. Having two on board meant a handoff could be made to the second helo, so any contact could be pursued non-stop for considerable lengths of time.

The Navy first looked at trying to fit the carrier based SH-3 Sea King helo onto escorts, but that LAMPS II program was soon shelved.

The Navy had kept a close eye on the US Army’s  UTTAS competition to field a replacement for the UH-1 Huey, which eventually resulted in the UH-60 Blackhawk helicopter. Early on, the Navy asked for a proposed naval variant, with folding rotors, a folding tailboom, and extensive corrosion proofing (salty sea air is tough on airframes).

The resulting SH-60B Seahawk featured a more capable datalink, TACNAV system, and associated ASW equipment. Further, the datalink allowed the radar video to be transmitted back to the ship, allowing the Combat Information Center aboard to have a more complete picture of the tactical situation. Additional systems included an integrated Electronic Support Measures (ESM) suite. ESM detects, collects and analyses enemy radio and radar transmissions to passively sniff out enemy units.

In a first, the prime contractor for this LAMPS III program wasn’t the manufacturer of the SH-60B, Sikorsky. The need to integrate complex systems onboard the helicopter, and the host ship meant that IBM was the prime contractor, and the airframe was simply a product built by a subcontractor.

The SH-60B was a far more capable helicopter than the Seasprite. Bigger, with a longer range, and able to carry much more fuel and more torpedoes, the SH-60B was the primary ASW weapon of the destroyers and frigates it served aboard.  It is capable of prosecuting contacts up to 100nm miles from its ship for up to two hours.

About a decade ago, a modernization effort began to update the SH-60, resulting in the MH-60R that adds a dipping sonar, forward looking infra-red (FLIR)/laser rangefinder/designator and the option of carrying Hellfire missiles to improve its surface attack capability. The MH-60R is in production, and replacing the SH-60B.

In recent years, the emphasis has shifted from hunting Soviet nuclear subs in the open ocean at long ranges, and instead hunting quiet diesel electric subs in the shallow waters of the littorals, The MH-60R is better equipped to deal with this threat.

As sensors improve, the weapons of the surface ship will continue to evolve to provide the punch against subs. As the Navy deploys unmanned surface vehicles and unmanned underwater vehicles, it is likely that at some point, they will be weaponized to serve as the surface ship’s battery against the submarine threat.

Surface Anti-Submarine Warfare Weapons- Stand-Off Weapons- 1 of 2

World War II sonars had a maximum effective range of roughly 2000 yards. Given that wartime submarine torpedoes were rarely effective past about  that range, and indeed usually used much closer, that wasn’t a terrible problem. But submarine sonars, and passive hydrophones, being submerged deeper, almost always provided better detection than surface escorts.

The trend in post-war escorts was to use more powerful, larger, lower frequency sonars, which gave better detection ranges. The first in wide use with the US Navy was the SQS-4 series, with a range of 4500-5500 yards. Later the SQS-23 series, a massive sonar housed in a dome at the forefoot of a ship’s bow, could, under ideal circumstances, achieve detection out to as much as 40,000 yards. More typically, the  -23 could reliably detect submerged targets from 10,000 to 20,000 yards.

While the lightweight homing torpedoes discussed in the previous post were quite capable, they had one glaring shortcoming. By the time an escort was in range to use them, they were already well within range of heavier submarine launched homing torpedoes. A means of extending the range of surface ASW weapons, both to protect the escort, and to take advantage of increased detection range, was a high priority.

The first, most obvious idea was to use large diameter torpedo tubes to fire heavy homing torpedoes.  But the challenges of accurate fire control at extreme ranges meant heavy torpedoes were less than optimal. Worse, any heavy torpedo would simply reach a parity with any submarine torpedo. Something better was needed.

The US Navy had the bright idea to use a rocket to lob the Mk44 Lightweight Torpedo onto a sonar contact. Originally the Rocket Assisted Torpedo (RAT) was hoped to be a lightweight, rather simple system. A parallel program also was started to lob a nuclear depth charge. The minimum safe range of about 5 miles (~10,000 yards) mandated a far more substantial rocket. The programs were merged, with resulting ASROC (Anti-Submarine Rocket) becoming the primary US Navy surface ASW weapon from 1961 well into the 1990s.

An 8-cell “pepperbox” launcher would elevate and train for a simple ballistic, unguided rocket to drop either a Mk 46 torpedo or a nuclear depth bomb onto the enemy submarine. The ASROC maximum range of about 19,000 yards, combined with the range of (then) modern sonars gave escorts a good standoff weapon.

[youtube=http://www.youtube.com/watch?v=j_phy0f0e1Y]
[youtube=http://www.youtube.com/watch?v=2dTaSmTxpbM]

ASROC was also used by a great many allied nations, and continues in widespread use with other navies. Ships equipped with certain guided missile launchers could fire ASROC from them, obviating the need for the 8-round launcher. Alternatively, the 8-round launcher could be modified to fire Harpoon Anti-Ship missiles, and even the Standard Missile.

If the above videos are a bit long, here’s a quick video of loading and firing ASROC from a Greek destroyer.

[youtube=http://www.youtube.com/watch?v=hRqjTKzS1JU]

…..

The nuclear depth bomb variant of ASROC was only live fire tested once.

[youtube=http://www.youtube.com/watch?v=EV5q_mlhaiM]

—–

With the introduction of the Mk41 Vertical Launch System on Aegis cruisers and destroyers, a new version of ASROC, after a surprisingly difficult development, entered service.

But ASROC wasn’t the only way of launching a lightweight torpedo to a distant contact.

The Australians developed their own approach, with a rocket boosted radio controlled glider used to deploy a homing torpedo. Dubbed Ikara, this weapon had the advantage that the water entry point of the torpedo could be updated during the flight of the rocket. Slaved to the sonar fire control system,  this meant maneuvers by the target during the time of flight could be countered.

[youtube=http://www.youtube.com/watch?v=MmEq9hhEInw]

Ikara served with the Australians, the New Zealanders, and with the Royal Navy.

The French Malafon system operated on a similar principle.

On the Soviet side, the SS-N-14 operated on a similar principle, but had a much greater range. The terminal guidance could be made by an helicopter operating from the parent ship.

We will address shipboard helicopters in our final post in this series.

Surface Anti-Submarine Warfare Weapons- The Torpedo

The torpedo was the traditional main battery of the destroyer. But the straight running steam powered torpedo was an anti-surface ship weapon, with no ability to engage submerged targets.

To tell the story of the surface launched anti-submarine torpedo, we have to take a brief detour to an air launched ASW weapon.

Submarines in World War II were really more “surface ships that could dive for a little while to avoid radar or visual detection.”  As carrier based and long range land based patrol aircraft became available, they became the primary threat to U-boats. Ranging far ahead of a convoy, their mere presence could force U-boats to dive. With an effective speed of only 3-4 knots submerged, even a slow convoy with a speed of 7 or 8 knots could easily evade. But the allies wanted to kill as many U-boats as possible, obviously. So these airborne scouts would also attack, generally with the 325lb depth charge. As noted, the depth charge tended to have a low probability of success.

The Navy, in cooperation with Harvard, Western Electric, and General Electric devised a passive acoustic sensor developed a battery, electric motor (from a washing machine!) and steering system. Melded into one unit, it was the Mk24 Mine, code named “Fido.” The term “mine” was a deliberate ruse to conceal the fact that it was an air dropped passive homing anti-submarine torpedo.

http://i5.photobucket.com/albums/y153/Gromit801/WTUS_WWII_Fido_pic.jpg

The Mk24 had a 24% success rate (a phenomenal rate in ASW).

With a speed of about 12 knots, and a running time of about 10-15 minutes, when a patrol plane sp0tted a surfaced U-Boat, it would attack. If the U-Boat didn’t dive upon approach, an attack with guns or conventional bombs/depth charges would be made. When the U-Boat did submerge, the attacking plane would fly up the wake, and drop were the wake ended. That put Fido in the sweet spot to pick up the scent, as it were. To conceal that the subs were being attacked by a torpedo, pilots were forbidden to drop Fido until after the U-Boat submerged.

Mk24 was modified in a slightly larger version as M27 Cutie, for use by our submarines in an anti-shipping role. But oddly, neither variant was deployed by surface ships.

In 1950, an active acoustic sensor was introduced on what was essentially an improved Mk 24 body, introduced into service as the Mk 32. The Mk 32 had a greater range than the Mk 24. Rather than being launched from a tube, the Mk2 launcher simply flipped the Mk 32 over a ship’s side.

http://www.dd793.org/Weapons/tp-2.jpg

Eventually, the increased submerged speeds of submarines meant a new, much faster, deep diving torpedo would be needed.

As the Mk 32 entered service, development started on a “universal” lightweight homing torpedo, one that could be launched from surface ships, helicopters, and fixed wing ASW aircraft. The first was the Mk 43 Light Weight Torpedo. Rather confusingly, it was launched from the Mk 32 Surface Vessel Torpedo Tube (SVTT).

The Mk 32 SVTT is usually seen as a trainable triple tube mount (and is typically installed port and starboard on a ship), but fixed twin tube mounts have been used. Compressed air is used to eject the torpedo.

The size of the Mk 32 SVTT essentially fixed the size of future lightweight torpedoes. The Mk 43 torpedo was quickly replaced by the Mk 44, in turn replaced by the Mk 46, which is still in service, and the later Mk 50 and Mk 54 torpedoes.

We’ve focused here US weapons, but as a practical matter, the US was the supplier to virtually all Western nations through the 1960s. Soviet lightweight torpedo was generally similar.

Next up, low frequency long range sonars demand standoff weapons.

Surface Anti-Submarine Warfare Weapons- The US makes a misstep

While the US found Hedgehog sufficient during World War II, the advances in submarine technology at the end of the war such as air independent propulsion and high speed underwater hulls meant the Hedgehog would be incapable of coping with the future threat. And that threat was seen as a huge fleet of Soviet submarines.  Much of the surface fleet of the US Navy shifted to high speed specialized ASW platforms. And one of the key weapons seen as addressing the threat was a depth charge projector. The RUR-4, known as Weapon Able,* was, much like Limbo, tied into the ship’s sonar system to provide fire control.

Unlike Limbo, Weapon Able was overly complicated, and throughout its service had a reputation of being something of a maintenance nightmare.

[youtube=http://www.youtube.com/watch?v=KTvP2h1U2Bk]

While Weapon Able was mounted on quite a few ships, for the most part the Navy would soldier on with Hedgehog until it was replace by the next generation standoff weapons, the subject of our next post in the series.

*after the 1962 shift to an updated phonetic alphabet, it became known as Weapon Alpha.

Surface Anti-Submarine Warfare Weapons- Ahead Thrown Weapons

From the beginning of Anti-Submarine Warfare (ASW), the development of weapons has been largely driven by the development of sensors, particularly sonar.

In Part I, we noted the challenge that an attacking escort would have to pass directly over a submerged submarine in order to attack. Early active sonars worked much like a searchlight, with the beam being narrow in both azimuth and depression. A deep diving submarine would pass under this beam at often fairly extended ranges. This meant that from the time when contact was lost until the depth charges detonated, as much as a minute could pass, and the target could maneuver to avoid damage or destruction.

Hedgehog

The Royal Navy sought a way to deliver weapons to the target while it was still in sonar contact. Attempts at coordinated attacks with two or more escorts were tried, but the small number of escorts available, and the challenges of coordinating an attack made this approach less than successful. Ideally, a single escort would be able to gain contact, localize, track and attack a target without loss of contact.

There were attempts to develop an ahead thrown depth charge system, but that would have required a more powerful system than a K-Gun, and would have weighed far more. Worse still, when using conventional depth charges, the escort would be moving away from the blast. With an ahead thrown charge, the escort would be closing the blast. In the worst case scenario, an escort could sail over its own depth charge blast. And such a charge under the keep of an escort would be far more dangerous to the escort than to the target.

As with so many innovations in modern warfare, it was the British who devised a solution.  An officer of the Royal Artillery had been experimenting with ways to overcome shortcomings in trench mortars, and had devised a spigot mortar. Rather than having the round slide down a tube, the round instead went over a short spigot. This meant the size of the round wasn’t set by the size of the tube. A variety of warhead sizes could be thrown from any given spigot launcher.

http://www.home-guard.org.uk/hg/pics/spigot.jpg

While spigot mortars weren’t a wild success for ground combat, it didn’t take long for the Royal Navy to see the potential as an ASW weapon. By mounting 24 spigots on the foredeck of an escort, a pattern of charges could be thrown ahead of the attacking escort. As a bonus, the individual spigots could be arranged so the charges would land in a predictable pattern, either circular or elliptical.  Carefully timing the firing of the charges would mean the recoil forces would be spaced over time (meaning the ship would need little reinforcement, simplifying installation and needing less weight) and would cause all the charges to hit the water simultaneously.

Dubbed “Hedgehog” because the empty spigots resembled the spines of the critter, the ASW spigot mortar entered service with the RN in 1942, and quickly proved its efficacy. It was also rushed into production for the US Navy.

Each individual charge was roughly 32 pounds. Rather than using a time or depth fuze, Hedgehogs were contact fuzed only. If there were no explosions, the attacking ship knew it had missed. A single charge was usually sufficient to kill a U-Boat. With a range of roughly 250 yards, the Hedgehog allowed the attacking ship to launch before contact with the target was lost. The pattern was aimed by steering the entire ship.

File:Hedgehog anti-submarine mortar.jpg

File:USS Sarsfield (DDE-837) during ASW exercise 1950.jpg

Hedgehog was small enough that smaller escorts such as Destroyer Escorts and Corvettes could mount it. For smaller craft, such as US built PCs and SCs, a rocket powered variant, known as Mousetrap, was developed.

One advantage of the contact fuze was if an attack missed, the attacking escort could more quickly reacquire the target submarine. Roiling waters from depth charges gave many a U-Boat the chance to slip away. Hedgehog gave the U-Boats no such cover.

Developed to combat the scourge of the U-Boat in the Battle of the Atlantic, ironically, the most successful use of Hedgehog was by the US Navy in the Pacific. Melding splendid shiphandling, tactics, and signals intelligence, the USS England (DE-635) sank no less than six Japanese fleet subs in a twelve day period.

Variants of Hedgehog would remain in US Navy service well into the 1960s.

The Soviets took the idea of an ahead thrown contact weapon, and developed a series of RBU weapons using rocket projectiles. To this day, virtually every Russian warship has one or more RBU launchers.

File:RBU 6000.JPG

[youtube=http://www.youtube.com/watch?v=sdIvoPbpeyE]

Squid and Limbo

The Royal Navy had made significant improvements in sonar and underwater fire control. Automatic range and bearing recording were new capabilities. And the addition of the “Q” attachment to the standard Type 147 ASDIC (or sonar) gave accurate depth information of the target.  This allowed an escort to accurately track in three dimensions over time the position and course of a target. And that was more than just information, it was the first half of any fire control solution.

The answer was a weapon we’ve previously described as impractical, an ahead thrown depth charge. Named Squid, the depth charge mortar had three 12” tubes mounted inline, though with a slight variance, mounted on a rotating cradle. Each tube fired a 300 pound depth charge. Range of squid was roughly 275 yards. The slight variance in alignment of the tubes meant the charges impacted the water simultaneously in a triangular pattern. These charges were time fuzed by a clockwork mechanism to explode simultaneously. Most importantly, the timing was set automatically and continuously set by the fire control system until the moment of firing, giving far more accurate depth setting than any conventional depth charge system.

File:Squid Mortar.jpg

Squid was a very large, heavy system.  And the preferred installation was Double Squid, with two three-barreled mortars mounted. This meant a significant portion of an escort had to be devoted to the mountings, consuming valuable centerline space that would otherwise be devoted to gun mounts or torpedo tubes. For the RN, facing primarily a submarine threat in the Atlantic, this was an acceptable trade off. The US Navy, faced with air, surface and subsurface threats in the Pacific, found Hedgehog sufficient. Any redesign of escorts for Atlantic duty would have slowed production too much.

Double Squid fired two diametrically opposed triangular patterns superimposed. The first pattern was timed to explode 25 feet below the target depth, with the second triangle 25 feet above. The resulting “sandwich” shockwave was deadly to submarines. Of 50 Squid attacks in World War II, 17 destroyed the target submarine, a kill ratio of .34, far and away the most lethal system in use during the war. Squid remained in use in the Royal Navy until 1977.

Limbo (or ASW Mortar Mk 10) was a postwar development of Squid, with better range, heavier charges, stabilization for pitch and roll, and most importantly, automatic loading. Generally only a single Limbo was mounted, as the automatic reloading allowed rapid re-attacks. Limbo remained in use on British and Commonwealth ships until the 1990s.

Surface Anti-Submarine Warfare Weapons- The Humble Depth Charge

In spite of submarine warfare causing the British and French great distress in World War I, it wasn’t until 1915 that anyone came up with an effective means of attacking a submerged U-boat, the depth charge.

You’ve seen enough movies to have a basic grasp of what a depth charge is. A cylindrical container full of explosives rolled off the back of an escort ship that detonates when it reaches a preset depth, as determined by a hydrostatic firing device (know in the business as a “firing pistol” for some reason).

But simply rolling a few depth charges off the stern of a ship over the likely position of a submarine is very unlikely to yield any real effects on the target. Most depth charges weigh between 300 and 600 pounds. Roughly 1/2 to 2/3 that weight is explosive. And to be effective, a depth charge has to detonate within about 30 to 40 feet of the submarine. Given the extremely poor state of sensors in those days, coming that close would be more a matter of chance than tactics. Indeed, between 1915 and 1917, only 9 U-boats were sunk by depth charge.1 The linear pattern of depth charges meant a simple turn by the U-Boat could easily remove it from danger. The solution for the escort was to widen area covered by a single attack. Perhaps two ships could make parallel depth charge attacks? But there was seldom enough ships to allow this, nor were two ships likely close enough to be able to quickly coordinate an attack. Instead, the Y-Gun depth charge projector was invented.

The Y-Gun was basically a mortar with a single charge firing into two tubes arranged in a Y-shape. In each of the tubes was a piston that ended in a broad curved “lear” (leading to the pistons being know as arbors) that nestled a depth charge. Mounted on the centerline of a destroyer, when fired, a Y-Gun would send a depth charge about 40-50 yards to both port and starboard of the ship.  Even such a modest increase in the square area of a depth charge pattern greatly increased the likelihood of a successful attack.

By the end of World War I, most destroyer types had at least one and and usually two Y-Guns aboard.

By the beginning of World War II, active sonar had improved to the point that, while not terribly effective as an area search weapon, it provided decent bearing and range information for an attacking escort. But ASW planners failed to understand the importance of determining the depth of a target sub.  Some estimation could be made. The shape of the sonar beam and the way it angled through the water could provide a very rough trigonometric estimation of depth.  The other serious improvement in technology was the rather simple idea of splitting a Y-Gun in half. The K-Gun fired one charge to one side. The advantage of this was that K-Guns could be mounted along the sides of an escort without displacing other weapons from centerline space. Even relatively small escorts could carry four, six, even as many as ten K-Guns. Combined with two chutes of depth charges, a pattern of charges could be laid on the suspected position of the target sub.

The uncertainty of the depth of the target meant that in addition to charges being delivered along the path of the attacking escort, and to the sides via the K-Guns, the attack had to be delivered at varying depths as well.  Eventually the standard attack would evolve to be a “10 charge” attack. Essentially, two overlaying diamond shape patterns (with a fifth charge in the center) at two depths, above and below the suspected depth of the sub, to sandwich the target, or catch it as it attempted to turn away.

This double diamond attack was by far the most effective depth charge of the war. It had a whopping 5% success rate of sinking or seriously damaging its target.

One of the most serious shortcomings of the depth charge as an ASW weapon was that the attacking ship would lose contact with the target, depending on its depth, at a range of from 200 yards clear out to as much as 500 yards. Counting the time needed for the ship to travel that distance, and the further delay for the charges to sink, the target sub had significant time to maneuver to escape. And the explosion of the depth charges roiled the water, meaning reacquiring the target was problematic at best.

[youtube=http://www.youtube.com/watch?v=gPGLwAlxBdM]

Later, we’ll look to weapons and sensors that addressed these shortcomings.

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1. Indeed, between 1915 and 1917, only 9 U-boats were sunk by depth charge.

It’s Corvette Week at CIMSEC

And Chuck Hill has a nice piece to start us off with, asking (and answering) the most basic question- just what is a corvette?

Classification of surface warships as cruisers, destroyers, frigates, or corvettes, has become like pornography. There are no generally accepted definitions, but “I know it when I see it”–except that everyone sees it a little differently.

Since this is “Corvette Week” what are we really talking about?

(Note: unless otherwise specified, lengths are over all and displacements are full load)

My Combat Fleets of the World, 16th Edition, which I have used here extensively for reference, defines Corvettes as, “Surface Combatants of less than 1,500 tons but more than 1,000 full load displacement–essentially, fourth rate surface combatants.”  but goes on to note that “…the designation as used here essentially refers to smaller frigates and does not correspond to the European concept of corvettes as any warship larger than a patrol craft but smaller than a frigate.” I feel to confine the definition within a 500 ton range is too restrictive. in fact it would have excluded the Castle class corvettes of WWII as too large, and other corvettes as too small.

I’ll just note that in our Navy, typically the smallest surface combatant we’ve built in peacetime is the Frigate or (as designated prior to 1975) the Destroyer Escort.

Our Navy currently is pretty well stocked with Destroyers, with some 62 of the excellent DDG-51 class in service. But our Frigates of the FFG-7 class are nearing the ends of their service lives. The LCS is being built, but since day one, Big Navy has denied the LCS is a replacement for the Frigate.

And to a great extent, that’s true. Our Frigates, while always general purpose warships, have been optimized for the open ocean Anti-Submarine Warfare (ASW)  role.

With the collapse of the Soviet Union, the blue water ASW mission has declined greatly. But there is still a pressing need for a numerous class of warships to fulfill missions that don’t require the capability of a multi-billion dollar DDG-51.

Is there a place for a low-end corvette combatant in our Navy? What roles and missions would it perform? Where is it likely to serve? How should it be armed?

Hopefully, the Corvette Week series at CIMSEC will provide answers to those questions.

A Good Primer on the Mission Modules for the Littoral Combat Ship Program

One of the key innovations of the Littoral Combat Ship Program was to be a series of plug-and-play modules that would tailor the ship’s capabilities to a given mission. Much as adding pods and armament to an airframe can change an airplane mission set, the goal was to have a bare bones seaframe that could accept modules that would fulfill one of three common surface warfare missions- Anti-Mine Warfare (MiW or MCM for Mine Counter Measures), Anti-Surface Warfare (ASuW) or Anti-Submarine Warfare (ASW).  The concept of operations originally called for these modules, and the specialist crews for them, to be forward deployed to advanced bases. Modules and personnel  for one mission would be swapped out for the modules and crew of another in as little as 24 hours. Alas, certain programmatic failures have precluded that from happening, but the basic idea of mission tailored modules endures.

In a smart program management world, the PM would have noted that virtually every module set includes new, untried technologies still early in development. And the smart PM would have developed prototypes of each component for each module, and then sent those prototypes to sea on existing platforms, such as Perry-class FFGs, or Burke-class DDGs to identify strengths and weaknesses, as well as previously unforeseen challenges. Having prototyped and tested the components, prototype modules could then have been sent to sea for a similar evaluation.  Having developed a level of technical maturity, the PM could then have solicited designs for the ships optimized to carry and employ these modular weapon sets.

But that’s not what happened in the LCS program. Instead, the Navy laid down very ambitious (and largely unjustified) requirements for what the seaframes could do, and set aside seemingly arbitrary requirements for power, cooling and space for modules, which the PM office seemed to simply assume would proceed through development with no major issues.

We’ve written enough times about the LCS seaframes themselves (and likely will do so again). But we’ve paid scant attention to the development of the modules that will (in theory) make the LCS more than an overly large patrol boat.

Anti-Submarine Warfare Package. Government Accountability Office Graphic

USNI News hase a great overview of the status of the mission modules.

The beating heart of both variants of the littoral combat ship (LCS) is the series of three mission packages the Navy is developing to handle some of the service’s most dire needs in the littorals.

The modular ship is a marked departure from the past in the way the Navy develops capability for its surface fleet. Sailors often liken the LCS to a video game system—with the mission packages being the actual games. But instead of “Halo” or “Call of Duty,” sailors will try their hands at mine countermeasures (MCM), surface warfare (SuW) and anti-submarine warfare (ASW).

On paper, the new capabilities and updates of existing functions will greatly increase the Navy’s ability to rapidly undertake some of its most dangerous jobs.

However, the mission packages have experienced delays of up to four years in fielding because of design problems, cost overruns, and manufacturing delays, according to the Government Accountability Office.

A July report from the GAO said, “a pause is needed” in the acquisition of the mission packages pending further review of the total LCS program.

“Navy has a great deal of learning to do about the ships, the integrated capability that they are intended to provide when equipped with the mission modules, and how the overall LCS concept will be implemented,” the report concluded.

On Aug. 8, USNI News interviewed Capt. John Ailes, program manager for Naval Sea Systems Command (NAVSEA) Program Executive Office Littoral and Mine Warfare’s (PEO LMW) LCS Mission Modules, for an update on the embattled mission package program.

Ailes acknowledged past failures in the program but painted an optimistic picture of the way forward for the mission packages.

“It’s a wondrous time to be the mission package guy today compared to three years ago because you can point to the successes,” he said.

Starting next year, the Navy will test the packages in a series of operational evaluations (OPEVAL) as a final examination before moving the new capabilities into the fleet.

Read the whole thing. There will be a quiz later. Oh, and take note of that last paragraph in the quote above.  The first two LCS ships have been in commission for years. And LCS-1 is currently on its first deployment. And yet, we’re still a year out from OPEVAL, let alone fleet introduction, of the modules.