Gunnery

For centuries, the main battery, or armament of naval warships was the gun. For most of that time, it was the relatively simple cast iron or brass  muzzle loading black powder cannon firing iron cannon balls at relatively short ranges. With the invention of smokeless powder, coupled with the introduction of quality steel, gunnery in the span of two generations or so made incredible leaps in range, accuracy and complexity.

The 16” naval rifles of the mighty Iowa class battleships are probably the most famous modern naval guns, but for my money, the pinnacle was reached with the automatic Mk16 8”/55 caliber guns of the Des Moines class heavy cruisers.

[youtube https://www.youtube.com/watch?v=ICifnf63lCs]

Only three ships of the class were built (the rest were cancelled with the end of World War II) but the USS Newport News would go on to serve until 1975, the last of the all gun cruisers in US Navy service.

Since the big gun cruisers are gone, current standard US Navy gun is the rather anemic Mk 45 5” gun, in both its 54 caliber and recent 62 caliber varieties. The M45 tosses a 70 pound projectile about 13 miles, and has a rate of fire of about 15 rounds per minute.

The Navy has invested vast sums over the  last 20 years or so developing the Advanced Gun System, a 155mm/62 caliber gun designed to fire the Long Range Land Attack Projectile, or LRLAP.

 

While the AGS and the LRLAP offer a substantial warhead with a range of about 59 miles, the problem is, the AGS can only fire the LRLAP. It cannot fire existing 155mm ammunition. That limits it to strictly a land attack role.

The Navy has been closely watching the performance of the Army’s guided Excalibur 155mm projectile. And they’re also looking forward to soon having a practical electromagnetic rail gun ready for sea. Now, a rail gun is pretty useless without ammunition. So the Navy decided to start looking for what could be used. They’ve basically decided to go with a subcaliber, saboted dart. The result if the Hypervelocity Projectile, or HVP.

[youtube https://www.youtube.com/watch?v=rIHMVtLNBzQ]

But this is where our story gets kind of interesting. Since guiding a gun projectile is something that has already been figured out, the Navy and its contractor, BAE Systems, decided to make the HVP guided. After all, great range is not worth a lot if there isn’t great accuracy on the impact end. And while the projectile is a good deal smaller than a 155mm round, they still found space to pack in a small bursting charge.

The Navy also pretty quickly realized that such a projectile could easily be adapted to be fired from not just a future railgun, but also its entire existing inventory of 5” guns. Even better, a version for the AGS could be built. And why stop there? Why not build a version for the Marines and Army 155mm artillery pieces?

HVP

[scribd id=265836810 key=key-W4wnIoURZ1SKfx9bSLP5 mode=scroll]

As Spill and I were discussing this yesterday, he brought up a very good point. While the program currently is for land attack projectiles, it’s not going to be very long before someone has the bright idea to use this as an Anti-Surface Warfare weapon. The gun has for many years been a secondary armament against ships, with the anti-ship missile forming the main battery. And while that’s likely to stay true, a 5” gun with a range of 50nm and a rate of fire of 20 rounds a minute is going to pose a real threat to any surface ship out there. One or two rounds probably won’t cause too much damage, but a series of hits would quickly place all but the largest ships out of action. Further, the HVP’s speed and small size means there will be little or no means to defeat it before it impacts the target.

It will be interesting to see what the next few years bring.

Couple Random Thoughts on Anti-Surface Warfare

We linked to this CIMSEC piece on integrating the P-8A Poseidon with a long range anti-ship missile a couple weeks ago.

Anti-Surface Warfare (variously abbreviated either ASuW or SUW) poses a few challenges. For the most part, it is likely to take place at over the horizon ranges. That is, from a surface ship perspective, the radar horizon, limited by the height of the antenna and the curvature of the earth, is fairly short, say 20~25 miles. Ships certainly can detect threat ships at longer ranges via passive measures such as radar warning receivers, such as the SLQ-32 or the SSQ-108(V) Classic Outboard. Passive sensors alert to the presence of a radiating warship, with some fair indication of bearing (~1 degree of accuracy) and some hint of range, based on signal strength. Cooperation between two receivers can generate a fair fix depending on the baseline and environmental factors. Maybe good enough to shoot, but hardly precision targeting.

A real challenge the US faces, especially in the littorals and the Western Pacific is the density of shipping there means that enemy warships will be intermixed with friendly and neutral merchant shipping, requiring a far more precise location, and positive identification of a potential target. As LT Rusty mentioned in the comments here, the surface Navy’s thinking around the turn of the century was that an actual positive Visual Identification (VID) would be required. The obvious problem with that is, anyone close enough to VID a target is likely to get smoked with a quickness.

There are other means of generating that identification. When you think of a radar return, you generally envision a glowing green blip on a dark radar scope. But most radars today convert the raw video to a graphic symbol. Other radars, however, have modes such as Synthetic Aperture Radar (SAR) or Inverse Synthetic Aperture Radar Mode (ISAR) that uses the motion of the radar platform or the motion of the target to artificially act as a much larger antenna. Through advanced signal processing, a three dimensional picture of the target can be derived and displayed, with enough fidelity to make a positive identification.  The P-8A is being equipped with a radar capable of doing this at quite long ranges. Optical sensors capable of extremely fine resolution at long ranges are another option, though whether they are capable of near-real time use is an open question.

Ohio State University Stadium SAR Image

Another problem is SUW is the time of flight for a weapon. During the lag from launch to arrival in the target area, the target itself is moving, and often in an unpredictable manner. The seekers of anti-ship missiles have relatively small fields of view.  A missile might completely fail to acquire a target, or acquire the wrong target, either another ship in an enemy formation, or worse, a completely innocent neutral ship. One of the great shortcomings of our currently fielded Harpoon Block 1C missile is that it is completely fire-and-forget. It goes where it was told before launch, and then starts its own search.  More modern missile (including the Harpoon Block II soon to enter service) can receive updates on the target location during flight, otherwise known as a mid-course update. Of course, that requires the target be carefully tracked by the launch platform or other sensor.

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Let’s talk about a missed opportunity.  A few years ago, Raytheon and the Navy had the bright idea to take some of its large inventory of older Standard SM-2 missiles and convert them to a land attack variant, known as SM-4 or LASM (the not terribly original Land Attack Standard Missile). Using a GPS/INS guidance system similar to that on the JDAM precision bomb, the LASM would have been a fairly cheap means of augmenting the striking power of destroyers and cruisers. The program was cancelled before any were fielded to the fleet, apparently for lack of funds, and because the LASM had a rather anemic warhead, one optimized for destroying airplanes, not land targets.

As n0ted in an earlier post, later Burke class destroyers have a limited SUW capability by using their SM-2 missiles against sea targets, rather than their intended air targets. But the semi-active guidance limits them to ships above the radar horizon. A variant of SM-4 with GPS/INS coupled to a anti-radiation seeker derived from the AGM-88 HARM could have given the surface fleet a viable over the horizon ability to at least damage enemy craft, at a relatively low cost.

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The Norwegians Konnsberg seems to nicely fit the bill as a replacement for a Harpoon sized missile.

[youtube https://www.youtube.com/watch?v=bzruKeRKA4c]

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For the foreseeable future, the US Navy’s primary anti-ship platforms will likely remain nuclear attack subs and strike fighter aircraft. And that is, to some extent, fine. They both have some advantages over a surface ship in terms of their abilities to engage, and to avoid engagement.

But as the emerging “distributed lethality” school of thought is beginning to recognize, presenting the enemy with multiple dilemmas (to steal a term from the Army’s current operating concept) has the advantage of forcing him to deal with multiple threats simultaneously, which means almost assuredly one threat is not adequately addressed. Giving tactical strike fighters, maritime patrol aircraft, subs, and the surface navy a viable capability to conduct offensive SUW at long range is itself a form of deterrence that minimizes the chance that the US Navy will ever in fact have to conduct such operations.

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.