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The modern escort warship


By Sakhal

The Task Forces of the United States Navy have their antimissile, antiaircraft and antisubmarine defense entrusted to the Ticonderoga-class cruisers (CG-47 onwards) and the Arleigh Burke- class destroyers (DDG-51 onwards), polyvalent ships provided with the AEGIS Combat System. These ships have a truly impressive combat power that surpasses that of many other contemporary designs.

The modern escort warship

Arleigh Burke class destroyer USS Donald Cook (photograph taken some time between 1999 and 2005).

The AEGIS Combat System (whose name was taken from the shield of Perseus) immediately detects any aerial or maritime element in a radius of up to 320 kilometers, even if it is so small as a bumblebee, and it is able to simultaneously detect and track several hundreds of echoes. Once it has checked the contacts analyzed by the IFF (Identification Friend or Foe) it assigns to each possible enemy a different danger level based on its type, distance, speed and many other parameters. In the Combat Information Center (CIC) the data is presented to the commander in multiple screens, in real time and scale, and he can decide if the counterattack will be effectuated in manual or automatic mode while giving or not the execution order. The AEGIS is constituted basically by the phased array radar panels (SPY), the computer equipment (UYK) and the missile launchers (VLS).

Phased array radars

A conventional radar rotates at a certain number of revolutions per minute, which increase as the echo gets closer. But since the rotation speed cannot be increased beyond a limit, in the face of threats able to travel 5 kilometers in just ten seconds, they are used instead fixed radars - whose emission and reception is constantly updated and transferred visually to large screens - which are formed by multiple panels, located in four positions in the ship in such a way that they cover the 360 degrees of the horizon, and at a certain height to have a larger detection field. The phase panels SPY-1, formed by a multifunction radar, are the core of the AEGIS. This radar combines horizontal and vertical search and effectuates the acquisition, classification and tracking of multiple targets, apart from the guidance of missiles. It works in S band, from 2000 to 4000 MegaHertz. Its wide, almost unlimited, capability of detection and tracking is in practice limited by the processing capability of the computers, making difficult to handle simultaneously more than several hundreds of contacts, while the capacity to guide missiles, counting with the support from the SPG-62, is of about 20 simultaneously.

Target illumination radars

As target illumination radar, the AEGIS uses the Raytheon AN-SPG-62 Mk 99, which is associated to the phase panels SPY-1 and specially adapted to the antiaircraft missile Standard SM-2. It works in X band, between 8000 and 12000 MegaHertz. The ships of the Ticonderoga class have four of these radars while those of the Arleigh Burke have only three. However these are equipped with the panels SPY-1D instead of the SPY-1A, as well as more updated combat systems.

Computers

Very powerful computers are in charge of analyzing individually each threat and comparing it with the rest, assigning it a level of dangerousness determined by diverse parameters. They are able to effectuate several millions of operations per second, to compute the diverse chances of success of each attacker. Once achieved the final result, according to the different options, they can start the attack automatically, taking control of the weapons to fire. When the first Ticonderoga was delivered, the configuration of her combat system was called Baseline 0, which used phase panels SPY-1A, twin missile launchers Mk 26 (for SM-1, SM-2 and ASROC), computers AN/UYK-7 and helicopters LAMPS I. The last model installed onboard the Ticonderoga was the Baseline 4, which was installed as well in the first Arleigh Burke. At the dawn of the 21st century, the Baseline 5 was being installed in the DDG-57 to 78, to be followed by the Baseline 6 which would use phase panels SPY-1D(V), Theatre Ballistic Missile Defense (TBMD), Advanced Tomahawk Weapon Control System (ATWCS), optical panels AN/UYQ-70 and missiles ESSM (Evolved Sea Sparrow Missile), to be installed in the DDG Flight IIA (DDG-79 to 92). The Baseline 7 would incorporate a good number of updates, specially regarding the computer, which would pass from the AN/UYK-44 to the COTS (Commercial-Off-The-Shelf). As comparative parameter, it would be interesting to mention that the Baseline I used a software of 820,000 instructions, while the Baseline 5 III uses one of 6.5 millions.

VLS launchers

The classic missile launchers used to be twin and rotatory and reloaded by complex mechanisms. It is a slow system to aim and reload and therefore uneffective in the defense against saturation missile attacks. Because of this it was adopted a system of multiple silos in which missiles of diverse types can be stored, being possible to fire them simultaneously for the current technology allows to effectively direct missiles even if the targets are illuminated at brief intervals. Generally, inside the cells on a Mk 41 VLS are stored antiship missiles Harpoon, antisubmarine missiles ASROC, cruise missiles Tomahawk, antiaircraft/antimissile missiles Standard and others like the most recent ESSM and Aster 15/30. A Mk 41 VLS module comprises eight cells, so a battery will have always a total number of cells which is a multiple of eight, being three cells reserved for the crane used for emergency sea service. In the Ticonderoga are used two twin batteries with 61 cells each, while the Arleigh Burke have one of 61 and another of 29. In the event of an attack it will be possible to fire the number of missiles desired, but the launchings should be made with small intervals, for the possible interferences in the trajectories of the missiles advise against totally simultaneous launchings.

The Ticonderoga cruisers

This series of 27 ships was built between 1983 and 1994 and, in a first moment, it was thought to propel them by means of steam turbines associated to nuclear reactors. But the high cost of such system forced to equip them with conventional propulsion of four gas turbines. These ships were projected from the hull of the Spruance class (DD-963 onwards), to which some modifications were made to compensate the increase in displacement (of about 18 percent). The increase in draught (of about 70 centimeters) forced to add a bulkhead in the fore part, reaching to the cannon mounting, to keep the prow as dry as possible. Other internal changes included the adoption of kevlar to reduce armor weight. The installation of the AEGIS and later the VLS increased the requirement of electric energy, which forced to use gas turbogenerators, increasing power production from 2000 to 2500 KiloWatt, but in turn demanding larger amounts of fuel to keep an acceptable operational range, which added extra weight.

Originally these ships were considered guided missile destroyers (DDG) to be later reclassified as guided missile cruisers (CG) before the entry into service of the first unit. During the "100-hour War" against Irak (operations Desert Storm and Desert Shield) these ships fired 105 Tomahawk missiles against ground targets. They are the first warships in the US Navy equipped with the AEGIS Combat System (before, the aircraft carrier USS Enterprise and the guided missile cruiser USS Long Beach, both of nuclear propulsion, had served as testing bench for the preceding system SCANFAR), which grants them a voluminous and characteristic silhouette. They have cooling filters in the gas exhausts to reduce infrared signature, as well as the Prairie system, which produces air bubbles beneath the hull to mask the own noise emissions.

The modern escort warship

Ticonderoga class cruiser USS Lake Champlain in 2003.

The Arleigh Burke destroyers

These missile destroyers were projected to replace those of the classes Charles F. Adams and Coontz, the first genuinely built missile cruisers in the US Navy, which were decommissioned during the 1980s and early 1990s. Originally, during Carter's presidency, it was expected to build a total of 49 units, which increased to 63 during Reagan's mandate. Finally the high cost of these ships, about 1000 millions of dollars each, reduced the expectations to 28 ships of the Flight I/II, plus about 14 of the Flight IIA. They entered service in 1991 and, as 2016, 62 units have been completed so far, being all of them in active service. The project was controversial because due to monetary reasons the helicopter hangar was suppressed - and later introduced from the Flight IIA -, so these ships could operate with the imprescindible SH-60 Seahawk LAMPS III, being able to refuel and rearm - but not maintain - them. From the Arleigh Burke derived the Kongo class, four ships in service with the Japanese Navy.

The modern escort warship

Arleigh Burke class destroyer USS Curtis Wilbur in 1999.

The propulsion power

Undoubtedly the propulsion plant is one of the most important elements onboard a warship. Still during the Second World War both speed and maneuverability probably constituted the best defense of a worthy warship. Because of this during the first half of the 20th century were built warships that sacrificed much for the sake of speed. Following the implantation of radar-controlled fire and missile systems speed lost much of that importance, but still nowadays it is one of the basic prestations listed in construction contracts and one whose reduction is not well received.

Nowadays, and despite not having the importance of former times, steam propulsion is widely used - in the form of turbines - by warships. Among these are all of those that use nuclear energy, for this one just replaces the traditional boiler which operates with fossil fuels (coal or petrol derivatives) by a nuclear reactor. During the last decades steam turbines, which are fast but demand much energy to operate, have been eclipsed by the more efficient gas turbines. Albeit the world of mechanical engineering experimented with this kind of propulsion even before than with the internal combustion engine, this system was not applied for the first time to a vessel until 1947, in particular to the British motor gun boat MGB 2009. Since then gas turbines have been widely perfected and nowadays they are one of the most used systems in fast warships, for their versatility, quick startup and strong acceleration render them as essential in any modern escort ship, be it a cruiser, a destroyer or a frigate. Gas turbine propulsion allows to pass from cold engine to full gas in only 90 seconds with an acceleration never seen before in marine ambients. The model LM2500 manufactured by General Electric became the leader in the world market, but other models like those made by Rolls-Royce or the Russian ones are also important.

The modern escort warship

Arleigh Burke class destroyer USS Cole in 2002.

Hybrid propulsion

The fact that a certain propulsion system offers particular advantages but also inconvenients makes that warships, on which victory or defeat - or life or death - is set by a very subtle line, often make use of mixed propulsion systems, to get the best qualities of each type. Hybrid installations integrate in a same group diverse types of propulsion, allowing to use one or other - or both simultaneously - in certain moments. It became usual that escort warships use a gas turbine for cruising speed and another one of greater power to move at full speed. As we can see, hybrid propulsion does not necessarily involve different types of engine, but can use also variants of a same engine type.

The modern escort warship

Arleigh Burke class destroyer USS Roosevelt in 2004.

Energy consumption

One of the characteristics of modern warships are their large requirements of electric energy. The production of such energy should have a good margin above the current requirements when a ship is designed, for a future weapon system could leave energy production at a tight level, severely affecting the future of the ship. This could happen for example with the new high-energy laser weapons that the US Navy has been testing in recent years, for such weapons would require brief but huge consumptions of energy. Because of this, it was thought seriously about the adoption of electric propulsion in warships, to take benefit from the surplus of electric energy delivered by the powerful generators that would be required to operate with such weapons. If the propulsion were integrally electric, there would exist the advantage of a more flexible internal distribution on the ships. Conventional mechanical propulsion makes use of many rigid elements to associate the diverse elements, but to connect electrical generators and motors only flexible wires are required.

The modern escort warship

Arleigh Burke class destroyer USS Halsey in 2011.

New missiles

During decades missiles have progressed much and modern missiles have little resemblance with the SS-N-2 "Styx" that in October 1967 sank an Israeli destroyer. Because of this modern warships incorporate the last achievements in antimissile defense, specially since "sea-skimmer" missiles appeared. The first missiles had a curved trajectory, ascending during launching and performing a parabola before descending at an uniformly accelerated speed against their target. These missiles could be detected relatively easily by radars, for they show up above the horizon and silhouetted against the sky. With the apparition of the modern sea-skimmer missiles which only ascend in the terminal phase of flight, when it is almost impossible to stop them, radars were rendered ineffective overnight, for the missiles were masked by the false echoes produced by the sea surface. Besides, radar waves do not follow the terrestrial curvature, and because of this a radar is more effective the higher it is located. Therefore the need of satellites and early-warning aircraft, which will help greatly to detect any type of missile, specially with the help of the Doppler function, which focuses in moving objects and filters stationary echoes.

Regarding antimissile defense, there is a further evolution of the fixed VLS mountings that fires only one type of missile and has generally a lesser number of cells. This new type of missile launcher has a "drum" which is orientable in azimuth and elevation like the traditional twin-arm missile launchers, but is fitted with multiple cells or "alveoli". This is the case of the Mk 49 launcher, which has 21 cells housing the short-range antimissile missile RIM 116A RAM (Rolling Airframe Missile). Another contribution to these systems is the Sea Ram Phalanx, a Phalanx mounting on which the Vulcan cannon has been replaced by a 11-cell RAM launcher, having its own Doppler monopulse radar as well as FLIR (Forward Looking Infra Red).

The modern escort warship

Arleigh Burke class destroyer USS Russell in 2011.

Categories: Naval Warfare, Ships, Missiles

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Website: Military History

Article submitted: 2016-05-26




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