Diesel-Electric Corvettes


This is from Carlton Meyer's new book:  The Spectrum of Future Warfare     

     One of the greatest threats to modern warships are diesel-electric "DE" submarines.  They use their powerful diesel engines to deploy, but switch to electric and run on batteries to hide.  They can only cruise six knots with battery power, yet they are nearly impossible to detect.  Compare the heat and noise emitted by a gas-powered lawn mower to that of an electric fan and you get the idea.  If they stop completely and sit on the bottom, they are impossible to find as they produce no propeller noise or water disruption.  DE subs can do this in straits or sea lanes and listen for the sound of large ships.  If one comes in range, it can float upwards to periscope depth and take a look, and fire torpedoes if it desires. 

     The only way to destroy DE subs is to catch them in route to their hunting grounds, or when they recharge their batteries every few days by running their diesel engines.  Another weakness is they have an endurance of only two months, meaning they need to visit a port or a submarine tender for fuel, food, and other support.  Finding and sinking DE subs requires patience and the right equipment.  Fixed-wing aircraft and helicopters can be used, but they have limited endurance and generate a lot of noise that warns DE subs to hide.  Surface ships have the same problem, their engine noise announces their arrival to submarines.

     Surprisingly, no navy has constructed a DE ship that can switch to quiet electric propulsion when hunting submarines.  This does not require the development of new technology, DE engines already exist on submarines and the US Navy's ocean surveillance ships.  A small ship is best for submarine hunting as they are quieter, harder to see on the surface, more maneuverable, and a smaller target for submarines.  While cruising slowly on electric power, a DE ship will produce no heat for detection at night or in poor daytime weather, which submarines may detect with infrared periscopes.  A DE corvette is an ideal size for a sub hunter, with a displacement of less than 1000 tons and a submarine hunting helicopter on board.

     A DE corvette will literally go fishing, silently cruising slowly on electric power or sitting still in an area DE submarines are thought to operate, just waiting for a DE sub to run its diesel engines.  DE corvettes may operate in groups where several fish for DE subs while another operates as bait at 20 knots on loud diesel power in hopes of enticing a DE sub to the surface.  Old stripped down destroyers may be employed as bait ships in this game.  DE corvettes may also form a screen whenever surface ships enter or depart port to protect them from attack.

    DE corvettes will also prove very effective in port defense, prowling silently on electric power while searching for small boats or anything along the shoreline indicating naval commando activity.  Silent DE corvettes are perfect for amphibious and special operations.  At nightfall or in fog, they can switch to electric to go silent and cold and come slowly over the horizon to the shore to pick-up or drop off reconnaissance or commando teams, then depart back over the horizon to safety.

     All corvettes need a stealthy design like the new Swedish Visby class (right), which has flat angles to reflect radar away from the sender.  Its hull is made of layered plastic to save weight and nearly eliminate a magnetic signature that most sea mines seek.  An added advantage is that the sun doesn't heat ship surfaces during the daytime, so it doesn't glow at night in infrared viewers. 

     However, the Visby is not diesel-electric, it is diesel-gas turbine.  This is common among corvettes since diesels provide great fuel efficiency, while gas turbines kick in for bursts of speed.  This allows the Visby to reach 35 knots, and is a great design at only 600 tons, but for a DE Visby corvette, a top speed of 25 knots is fine.  A speed of 35 knots is not needed, not for mine hunting, not for patrolling since it burns too much fuel, and not for anti-submarine warfare.  Ten knots will make little difference trying to avoid anti-ship missiles or aircraft.  It would only make a difference while pursuing small boats, but then it has a helicopter.  Finally, corvettes will operate in unfamiliar shallow waters with reefs, sandbars, and underwater rocks, so going fast is unwise.

     While running on electric, a plastic-hulled Visby will be safe from mines, since they are activated by magnetic signature or engine noise.  Homing torpedoes are acoustic, seeking a ship's engine noise or the water disruption caused by a high-speed ship.  Most types of anti-ship missiles, like Harpoon and Penguin, rely on infrared sensors.  The only signature a Visby type DE corvette will have is a radar reflection, and that is reduced by more than half by enclosing exterior systems and using angled flat panels.  It can be struck by wire-guided torpedoes, but a submarine must stay at periscope depth to guide those visually, and if a DE corvette turns away from the torpedo while opening fire, it will be a difficult to hit.  DE corvettes and all surface combatants should have rifle-size lasers mounted so that lookouts can instantly blind periscopes, aircraft, or whatever threat appears.  A visible laser is best so the threat can be instantly seen and targeted by gun crews and aircraft, rather than the traditional method of finger pointing.

     The only serious threat to DE corvettes are traditional weapons guided by the human eyeball.  This is why DE corvettes will be most effective at night, where they are literally invisible while running on electric once the captain announces: "Rig for ultra quiet, blackout, coolout, ponchos on deck."  Ultra quiet is common sense, and so are blackout conditions, but coolout and ponchos on deck?  Modern infrared sights are very effective, they can see a man standing at 2000 meters.  DE corvettes may operate very close to an enemy shoreline, approaching within meters to drop off or pickup reconnaissance or commando teams at night.

      Therefore, DE corvettes must conduct tests to eliminate their infrared signature.  Shutting off the diesels eliminates most all the signature, but what about stoves inside the ship, or the ships' heating system?  If it is below freezing outside, will the heated interior of a DE corvette cause the ship to glow?  While some things can be insulated like computers, or located in a ship's interior, other steps may be required.  The ship's heating system may be cut off, or turned down.  Air conditioners may be shut down as they produce heat as well, and outside air vented through the ship.  Crewmen should remain inside the ship, but if they need to venture outside to help commandos aboard or to fix something, they must wear ponchos lined with special insulation to hide most of their body heat from detection, as described in this article: combat ponchos.

Corvette Tenders

     If a navy plans to conduct expeditionary or amphibious operations, it will need to deploy DE corvettes and sustain them in remote locations.  Small ships are difficult to maintain forward-deployed since they lack much of the organic maintenance support and crew comforts of larger ships.  Therefore, corvette squadrons need tenders, like the recently retired Yellowstone Class AD- 41 destroyer tender. (below)  A deployed squadron needs two tenders to keep one on station while the other journeys to a distant port for replenishment.  The squadron headquarters will remain embarked on the deployed tender, which will remain at sea with larger warships in high-threat environments, or in low-threat areas it may drop anchor in a small cove at an offshore island, although it may move every few days depending on the enemy threat.

      After a couple weeks on patrol, each corvette will tie up to its tender for a few days of rest, replenishment, and repairs.  These tenders can also support smaller patrol boats in their area, like the US Navy PC-1s.  In more lethal environments, the tender will have to remain far offshore with destroyers as corvettes pull alongside for just a few hours for replenishment and other urgent business.  During long deployments, the fleet commander will discover these tenders can help support his cruisers and destroyers too, making them even more valuable.

     Tenders will have specialized repairmen for the corvettes and a large spare parts block.  It will also host the squadron headquarters for the helicopters they embark, which will include a helicopter maintenance support section and large parts block.  The corvette squadron headquarters will oversee the personnel manning on each corvette, moving sailors who have conflicts to other boats, and providing replacements for sailors who are missing due to illness, injury, or leave.  The squadron will also maintain an emergency reaction team that can board a helicopter within minutes and fly off to assist a corvette that has suffered damage or causalities.

     Tenders will have a medical doctor, an operating room, a dentist, and the squadron personnel section to deal with payroll, legal, and career issues.  It will have a ship's store, a post office, a video game room, a gym, a running track topside, a barbershop, an ATM, a library, and Internet access when possible.  These may seem like luxuries, yet they are common on larger US Navy warships.  Tenders will have a cafeteria with fresh food, in contrast to the microwave meals served aboard corvettes.  Visiting tenders will be like a port call for corvette crews, so they should have bars with a four alcohol drink a day maximum.  Without such support, deployed corvettes cannot function after a few weeks, so Admirals will demand that they be replaced with large destroyers that have this support aboard ship.

      If the US Navy is short on funds for new tenders, it can activate two of the Yellowstone class tenders that were retired in 1996 and placed in a reserve status after just half their service life.  They can be upgraded and used another 30 years.  Tenders allow for smaller and less expensive warships by providing most all the non-combat support.  Tenders proved their value in past wars, and will do so again.

Problems with the LCS

      The US Navy is selecting a new type of coastal warship, called the Littoral Combat Ship. (LCS)   Details can be found here:  LCS.   The LCS is expected to accomplish these missions:

bulletAnti-surface warfare (ASuW) against hostile small boats
bulletMine Counter Measures (MCM)
bulletLittoral Anti-Submarine Warfare (ASW), and may include the following secondary missions
bulletIntelligence, Surveillance and Reconnaissance (ISR)
bulletHomeland Defense / Maritime Intercept
bulletSpecial Operation Forces support
bulletLogistic support for movement of personnel and supplies.

The US Navy needs dozens of Visby type DE corvettes, not an LCS design with these problems:    

1.  What  is an "LCS"?  Why does the US military have to abuse the English language by making up acronyms for everything?  The "LCS" is the size of a frigate with the mission of a corvette, so choose one of those English language terms. 

2.  While everyone likes the new Bofors 57mm naval gun, secondary armament is poor.  It consists of a .50 caliber machine gun on each side.  The first lesson learned from the deployment of the US Navy's newer PC-1 patrol boats was that basic .50 cal mounts and the unstabilized MK-38 25mm chain gun had horrible accuracy mounted aboard a small, bouncing ship.  As a result, the Navy developed a stabilized MK-96 25mm gun, which includes a 40mm automatic grenade launcher. (right)  In addition to the 57mm gun on the bow, the LCS should have one or maybe two of these weapons.  They should also have either an EFOGM video guided missile system, or a Hellfire laser-guided missile system.

3.  Where are the torpedo tubes?  One of the LCS missions is ASW, but it has no ASW weaponry.  Yes, it will have a helicopter, but what if the helicopter is broke down or off on a ferry mission?  What if the aircrew is asleep or operating 100 miles away and a submarine or incoming torpedo is spotted?  Most corvettes have torpedo tubes for ASW torpedos, the LCS must have at least two.  The LCS can carry the same lightweight torpedo as its helicopter, so its torpedo tubes are also magazines since those torpedoes can be removed and mounted on the helicopter if the situation warrants.  If ASW is not a current mission, it can save weight and deploy without torpedoes. 

4.  Who thought up this maximum speed of 40-50 knots? This isn't a cigarette boat for teenagers.  A 2003 analysis by David D. Rudko noted that the Navy has stated the LCS must incorporate endurance, speed, payload capacity, sea-keeping, shallow-draft and mission reconfigurability into a small ship design.  However, constraints in current ship design technology make this desired combination of design characteristics in small ships difficult to realize at any cost.  Speed, displacement, and significant wave height all result in considerable increases in fuel consumption, and as a result, severely limit LCS endurance. 

     When operating in a significant wave height of six feet, regardless of the amount of fuel carried, the maximum endurance achieved for a wave-piercing catamaran LCS outfitted with all modular mission packages is less than seven days.  Especially noteworthy is that when restricted to a fuel reserve of 50% and a fuel carrying capacity of Day tanks, the maximum achieved endurance is only 4.8 hours when operating at a maximum speed of 48 knots. The LCS can achieve high speeds, however, this can only be accomplished at the expense of range and payload capacity.

    The requirement to go fast requires a seaframe with large and heavy propulsion systems. The weight of the seaframe, required shipboard systems (weapons, sensors, command and control, and self-defense) and modular mission packages accounts for 84% of the full displacement, and as a result, substantially limits total fuel carrying capacity.  Since initial mission profiles required the high-speed capability less than 5% of the time, the end result is a ship that has very little endurance and a high-speed capability it will rarely use. Refueling, and potentially rearming, will require the LCS to frequently leave littoral waters and transit to Combat Logistics Force ships operating outside the littorals for replenishment. 

     In addition,  big engines and a heavy frame make a coastal ship far too big.  Look at all the other modern coastal ships around the world to discover the LCS is twice their size.  Twice the size means twice the target and twice the cost, all this for high speed?  The LCS is the size of modern frigates and bigger than destroyers of World War II, yet has the armament of a patrol boat in order to accommodate the mysterious ultra high-speed requirement. 

5. The LCS is not diesel-electric; it must be. 

      The US Navy should scrap the current LCS plan in favor of slower, smaller, and more capable DE corvettes based on the Visby class corvette design and supported by tenders.

 2008 www.G2mil.com

Nov 16, 2013 - Yes We Can, Build an Excellent Ship

Our Navy's attempt to build a coastal ship failed before construction began. I wrote an article about the proposed "LCS" back in 2008 that highlighted problems and the GAO produced several reports about this disaster.

I assumed the USA had become too corrupt to build a decent warship. However, I just learned that the USA is building an excellent coastal ship in Mississippi, for Egypt! As part of American military aid, the USA contracted to build four excellent Ambassador MK III ships (pictured). These 200 ft long craft are referred to as "missile boats" for political reasons. They are one-sixth the size of the LCS, cost half as much, are just as fast, and have twice the weaponry!

Since the Ambassador is much smaller, it is much more difficult to track and hit with weaponry, and has half the draft of the LCS, which is extremely important for a coastal craft. It does not carry two helicopters like the LCS, but those should operate far offshore, otherwise they help an enemy locate and target the ship. There have been no reported problems with the Ambassador since our Navy did not spend a billion dollars and a decade to "develop" it. Our foreign military sales office just chose a simple design using modern (proven) systems.

A dozen LCS have been funded thus far with four dozen more planned. Everyone is disappointed as they break down often and carry little weaponry. They don't even have basic Harpoon anti-ship missiles, and only a single 57mm deck gun, compared to the 76mm mounted on the Ambassador! Congress and the Navy would like to end LCS production, but our Navy would end up with few coastal craft since the frigates were retired early, assuming the big LCS counts as one since it is larger than WW II destroyers. The Ambassador class is under construction in the USA and provides a better ship at half the cost. Cancel the LCS program and buy four dozen Ambassadors!