Leptis Magna-class aircraft carrier (export variant)

This article is about the export variant. For the domestic variant, see Leptis Magna-class aircraft carrier.

File:LeptisMagnaCarrier.png CRS Leptis Magna in service colors.
Class overview
Name:	Leptis Magna-class aircraft carrier
Builders:	Mehmud-Tabnit Oran Shipbuilders Mehmud-Tabnit Lagos Shipyards United Nigerian Lagos Steelworks Philosir Industries Dakar Yards Santos de Cuba Guantanamo Navy Yard
Operators:	Carthaginian Navy Kouralian Royal Navy Republic of Vectors Republic of Krazakistan Kiburi Mwamba
Preceded by:	Hannibal Barca-class aircraft carrier
In commission:	2 March 2010
Planned:	96
Building:	10
Completed:	36
Active:	36
General characteristics
Class and type:	Leptis Magna-class aircraft carrier
Displacement:	109,500 tonnes
Length:	331.6 m (1,088 ft) (waterline) 363 m (1,190 ft) (overall)
Beam:	41 m (135 ft) (waterline) 80 m (263 ft) (flight deck)
Draft:	11.1 m (36.4 ft) (max navigational) 12.3 m (40.3 ft) (max)
Propulsion:	2 × IDOS Power Systems NCV4-C1S PWR (750 MWt, 262 MWe) 1 × United Nigerian PR-1400 gas turbine (100 MW) 4 × United Nigerian permanent magnet motors 4 × 4 m (13 ft) 7-bladed P7CR integrated motor-propulsors 320,000 shp (240 MW) 2 × 7 m (23 ft) Voith-Schneider propellers 40,000 shp (30 MW)
Speed:	34.5 kn (64.9 km/h) (max) 30 kn (56 km/h) (cruise)
Range:	20 year reactor life 50 year projected service life
Complement:	Ship's company: 2,500 Air wing: 2,400 Mission personnel: Up to 200 Max berth capacity: 6,000
Sensors and processing systems:	RAN-34 dual-band X/S search/tracking radar RAD-40 L-band air control radar
Electronic warfare & decoys:	6 × Super-rapid bloom off-board chaff launcher Multi-band EW suite Mk. 40 Surface ship torpedo defense system
Armament:	16 × Modular Mission Enhancement Package System-Combat (MMEPS-C) mounts
Armor:	30 mm spaced steel box around magazines and engines 70 mm kevlar over magazines, engines, and bunkers
Aircraft carried:	Up to 100 fixed-wing and helicopters
Aviation facilities:	4 × Electromagnetic Aircraft Launch System catapults 4 × Deck-edge elevator (3 starboard, 1 port) 2-level hangar with 2 centerline elevators to hangar deck

History

In 1995, the Carthaginian Navy embarked on the ambitious Naval Power in the 21st Century (NP21) project, a decade-long research, design, and development program with the goal of developing a new line of combatant warships to carry the navy into the new century. Major tenets of the program were to include interoperability and interchangeability of as many parts and systems as practicable to reduce maintenance costs, improved independent-action capability, improved combat endurance, and an increased tactical repertoire to better allow the navy to exploit any potential tactical vulnerabilities.

Much of the experience and lessons-learned that went into the project were derived from the Northern War of 1975-78, in which the three Ctesiphon Pact states of the Carthaginian Republic, the Russian Empire, and Inukiriniwdene fought the United European Federation, a member of the Montgomery Pact. The opening stages of the war found a large Carthaginian battlegroup of two supercarriers (one nuclear Hannibal Barca-class and one conventionalSyphax-class) plus one medium carrier (Libya-class) operating in the Norwegian and Barents Seas, where they had been conducting drills and trials with allied navies.

Although operations in the region were ultimately successful, with UEF Greenland and Iceland both seized and the battlegroup successfully returned to Carthaginian ports, the near-fiasco highlighted several potential shortcomings in existing doctrine and design. These included:

• Predominantly designed for the sunny climates of the Mediterranean and North Africa, the ships were demonstrated to be hampered in cold-weather operations, especially relative to Russian and Inuk designs. The ships were deficient in de-icing equipment, which slowed air operations below their nominal projected rate.
• Additionally, cut off from ready lines of supply, the ships were designed to only continue sorties for twenty days, but in practice, commanders estimated that after ten days of operations their existing reserves of spares could last only a few more days of continuous operations. This is despite the reduced sortie generation caused by the shortage of de-icing equipment.
• Despite the overwhelming quantity of air power possessed by the combined battlegroup, particularly in conjunction with Russian and Inuk escorts, the Carthaginian contingent lacked any capability to launch even small amphibious or aerial assaults. Initial air operations succeeded in suppressing the Greenland and Iceland air defense grids, but a lack of local marine support required the deployment of VDV paratroopers to exploit the vulnerabilities.
• Although possessing a theoretical maximum of 90 combat aircraft, the class encountered difficulty operating with any number over 80 aircraft, with additional planes creating flight deck and hangar congestion.

By 1995, when the NP21 project was beginning, the first of the Hannibal Barca-class carriers were also beginning to enter their scheduled Refueling and Major Refit (RMR). Originally planned for a 30-month cycle, inspections made in drydock revealed a host of additional complications that would push up overhaul costs and push completion dates back to a 36-month cycle. Thus, improved reliability became an additional priority of the design team.

Design

Hull design and construction

The hull of the existing Hannibal Barca-class was taken as a broad starting point. Service trials had already demonstrated that the fuller hull of the Hannibal Barca-class over the preceding Syphax-class was not fully offset by the improved length to beam ratio, resulting in a loss of speed. In order to rectify this perceived design flaw, the hull of the Leptis Magna-class was both lengthened and widened, but fineness was increased, returning to a more cruiser-like hull form with superior hydrodynamics and with a net increase in usable internal volume.

Above water, a new emphasis on radar cross-section reduction was instituted, transitioning the island from the conventional flat-sided tower to a well-angled version designed to minimize reflections. Similar changes were made to all other external surfaces, and as much external equipment as possible was either moved to internal storage or faired over with a low-RCS covering. Wider use of radar-absorbent material was considered, but was not approved on the grounds of cost for such a large warship as well as the durability needed to sustain air operations on the flight deck.

To offset the increase in length, weight-saving measures were instituted to keep displacement inflation under control. Many of the external fairings are composed of carbon fiber paneling or take advantage of other non-metallic polymers, with the added advantage of reducing vulnerability to salt water corrosion. By replacing these and certain other elements with lighter weight composites, an estimated 5,000 tonnes of projected weight increase was avoided, improving seakeeping and energy efficiency.

Combined, these features are estimated to reduce radar cross-section by some 60% and infrared emissions by some 80%, while increasing useful volume by 8% and allowing for a 2.5 knot speed increase over the previous class in spite of requiring only 40,000 additional shaft horsepower. Lifecycle costs are estimated to be some 20% lower than a first-generation nuclear aircraft carrier, and crew requirements significantly decreased.

Powerplant

With global commitments to its Ctesiphon Pact allies but no major bases outside native North African territory save Cuba, nuclear power was the favored powerplant solution for the NP21 project. However, unlike previous nuclear warships, the ships of the NP21 program were designed to use integrated electric propulsion, coupling the reactor's steam turbines directly to a set of generators, rather than to the drive shafts and propellers. This was the result of several requirements, namely the need to produce large quantities of electricity for the EMALS catapults and high-power radar and the modularity of the NCV4-series reactor plant.

Each of the two NCV4-C1S pressurized water reactors is integrated into a self-contained 'power pod,' including the reactor vessel itself, coolant loops, steam turbine, and electric generator. Thus, each pod requires only a supply of water for the secondary cooling loop and outputs electricity directly to the ship's power mains. This simplifies maintenance, in particular the Refueling and Major Refit, as the entire pod can be removed and replaced and allows the reactors to be run independently of the propellers. Survivability in the event of damage is also improved, since any contamination that breaches the reactor vessel would be contained within the pod itself.

Compared to the older NCV2-series reactor in the Hannibal Barca-class, the NCV4 is much more powerful despite its more compact footprint. Higher power densities and more efficient conversion equipment give each plant a rated maximum thermal output of 400 MW, of which 190 MW can be converted to electrical power. This means a single reactor can power the vessel up to 30 knots alone, while both reactors together have more than 130 MW of additional power for the ship's systems. Lifespan for each core is expected to be 20 years before scheduled RMR, although continued operation will result in only 10% power loss over the following five years, allowing maintenance to be deferred if necessary.

Supplementing the reactor plant is a 100 MW PR-1400 gas turbine engine, derived from R905 core used in the RTS-224 strategic transport. Under normal operating conditions the PR-1400 is not used, but functions as a backup to provide power in the event of a reactor shutdown or to supplement reactor output in other situations. The multi-fuel turbine is multi-fuel capable but normally run on jet fuel from the ship's aviation bunkers. A supplementary power source was required to provide cooling power in the event of a reactor shutdown. Alone, the turbine can power the ship to up to 26 knots, and with a full bunker of fuel, is rated for 12,000 nautical miles.

Electricity is distributed from the central plants via a multiply-redundant series of mains. In addition to this built-in system, a casualty power system allows for the use of large substitute cables to be plugged into fixed outlets throughout the ship, allowing for the manual rerouting of power around damaged sections. This also allows the ship to send and receive power from external sources, such as when providing assistance for humanitarian programs or when in port, allowing the reactors and turbines to both be shut down for servicing while the coolant pumps are run via external power.

Propulsion

Of the three major propulsion systems considered, pump jets were selected for their development potential and reduced vulnerability relative to other drive types. By moving the water flow into the hull and removing the need for long propeller shafts, the system was be made more durable and lighter in weight while also reducing acoustic detection potential. The loss of internal space to the intake gullet and expulsion systems was offset by the space gains from the removal of the shaft and gearing systems.

A rimless screw-type propeller was chosen for the pump-jet, removing the need for an internal shaft arrangement. Tests demonstrated that a center-driven propeller created unwanted turbulence around the shaft, reducing propulsive efficiency. The removal of the center shaft also allowed for the use of a more efficient screw propeller as the hollow center allows water to feed into the later stages of the propeller directly, increasing expulsion velocity and thus propulsive efficiency. Instead, the propeller is rim-driven by a permanent magnet motor, resulting in a nearly silent propulsion system.

To counter another major issue in the design of pump-jets, a soft durameter polymer was added to the upper wall of the intake gullet. As ship speeds increase, increased water flow through the intake gullet reduces propulsive efficiency as pressure builds in the intake section of the system. At low and medium speeds, pressure from the intake gullet keeps the polymer in its housing, but at higher speeds, water flowing into the gullet cannot quickly make the angled transition into the gullet, creating a negative pressure bubble which pulls the polymer out, forming a constricting barrier. This barrier reduces water flow into the gullet, thus reducing pressure on the propeller and improving high-speed efficiency.

Steering at high speed is accomplished through a combination of venturi vanes mounted on the pump-jets and a pair of conventional rudders mounted further aft. The steerable vanes allow all of the ship's thrust to be vectored, greatly improving maneuverability over conventional designs. The rudders serve to counter the Coandă effect inherent in pump-jets as well as provide additional emergency braking power by increasing the ship's drag. Between these two systems, the Leptis Magna-class is an extraordinarily agile ship for her size, aiding in torpedo defense and combat maneuvering.

Low-speed steering, where pump-jets are generally poor performers, is accomplished with a pair of retractable Voith-Schneider propellers located along the ship's centerline. These two propellers are capable of fully steering and maneuvering the ship in any direction at a speed of up to five knots, allowing the ship to dock and undock itself under its own power. Outside of port, the propellers are retracted into the hull, and are stored in the space between the outer and inner bottoms, retaining the ship's watertight integrity in the event of potential damage to the system.

Armament

A major feature of the NP21 warships is the development of a modular armament system for secondary weapons. The Leptis Magna-class is a beneficiary of this program, dubbed the Modular Mission Enhancement Package System (MMEPS), which allows her armament to be replaced within minutes via crane or heavy-lift helicopter, the new modules slotting into the standard Stele integrated combat management system. This allows malfunctioning modules to be replaced with a working unit while the original is repaired ashore, as well as outfitting the armament for specific threat environments.

Experience in the Barents Sea against large numbers of Exocet-armed UEF warships contributed to the greatly enhanced armament of the Leptis Magna-class, and most NP21 warships. The three Carthaginian carriers were successfully returned home in the face of such attacks only due to the valiant efforts of the Russian defense screen and command of the skies. Despite this, one Exocet did manage to strike Syphax, which was saved only by the missile's faulty detonator, a stroke of good fortune that could hardly be relied on for future engagements.

As a result, the Leptis Magna-class has positions for sixteen MMEPS-C mounts, three pairs on the starboard side, one pair directly aft, and four pairs on the port side. This represents a 50% increase over the previous Hannibal Barca-class, itself a 50% increase over the Syphax-class, without factoring in improvements to the weapons themselves. The standard outfit for a Leptis Magna-class carrier is for a paired arrangement of one Aspis CIWS mount and one Xiphos interceptor missile mount. Each has onboard engagement radars allowing autonomous target acquisition and engagement against targets within each unit's sector, although they are also networked into the ship's combat management system to maximize efficiency.

The Aspis CIWS mount is armed with a 35 mm autocannon with a maximum engagement range of 3,500 meters, and an 11-cell rolling airframe missile launcher with a maximum engagement range of 10 kilometers. The autocannon is fed by a 250-round on-mount ready magazine plus an additional 2,000 rounds stored in the modular base, usually a mix of supercavitating armor-piercing and fragmentation rounds for use against both soft and hard targets. The Xiphos interceptor missile rack houses eight missiles on each module with a maximum engagement range of 24 kilometers. It is optimized to engage both aircraft and supersonic sea-skimming missiles with a high degree of accuracy, although performance is enhanced in conjunction with the more precise shipboard radar suite.

As the units do not require deck penetration in their standalone mounts, they can be attached directly to the flight deck if additional armament is warranted, although this has never occurred in Carthaginian practice as it reduces usable flight deck space and can impede maximum flight efficiency. Standalone CIWS units also do not benefit from the additional round storage of the modular base, and still require electrical and data connections to the ship's systems.

Other MMEPS-C mounts can be used to alter the design armament, including torpedo launchers, anti-ship missile batteries, and even a light naval gun, although none of these are generally recommended for carrier use and are usually shipped only on surface warships.

Underwater

For sub-surface engagements, the Leptis Magna-class is equipped with two Mk. 40 Surface Ship Torpedo Defense Suites, each composed of a towed passive sonar array to detect potential threats, a towed acoustic decoy, and six deployable standalone acoustic decoys. The towed sonar array is optimized to detect incoming torpedoes over enemy submarines (although it can detect both) and can use the ship's onboard computing power to screen contacts to identify specific makes, models, and attack patterns (if known).

Upon torpedo detection, the system can either automatically deploy a towed or standalone acoustic decoy, modulating the emitted sound to match that of the ship, or deploy an interceptor torpedo from one of two six-round racks mounted low in the hull. Acoustic decoys are generally preferred as resolving the incoming torpedo salvo to sufficient clarity to deploy an interceptor torpedo requires additional time in a situation where such is generally in short supply, although certain types such as wake-homing torpedoes may not be fooled by acoustic decoys.

As a final line of defense, the supercavitating ammunition used in the Aspis mounts makes them capable of firing on incoming torpedoes if a sufficiently precise lock can be achieved.

Aircraft and boat handling

File:Carrier from Carthage.png

Diagram of systems and arrangements.

The large flight deck is angled outward by ten degrees, and flight deck space was largely squared-off relative to previous designs in order to expand available space. Moving the island further to the stern allows for refueling and rearming operations to be consolidated forward with additional space, while the port side is now commonly designated for VTOL operations, either helicopters or embarked VTOL aircraft if supporting amphibious operations.

CATOBAR operations are supported by four Electromagnetic Aircraft Launch System catapults, using linear induction motors to rapidly accelerate aircraft to launch speeds. The large power draw from these motors is one of the primary reasons why integrated electric power was chosen over conventional steam. Much finer control of catapult power is possible using electromagnetic systems, allowing them to launch lighter and heavier payloads without damage to either the aircraft or the catapult. The use of EMALS also removes the need for bulky and complex steam lines from the reactor plant to the flight deck, freeing up space and reducing maintenance requirements.

Three electromagnetically-tensioned arrestor cables are used, mounted on the rear of the flight deck, along with deployable crash barriers in the event of uncontrolled landings. As with the EMALS catapults, these arrestor wires can be dynamically tensioned to allow lighter and heavier aircraft to be recovered, making the operation of light drones possible. Flight deck size also allows land-based tactical airlifters to be operated from the deck, so long as they are equipped for catapult landings and are capable of short takeoffs.

Four elevators (three starboard, one port) are responsible for handling movement between the hangar deck and the flight deck, each capable of handling two standard-size aircraft or loads of up to 250 tonnes. Additionally, three secured lifts are used to move munitions from the armory to the deck to arm and rearm aircraft for sortie. Unlike previous classes, the armory system is operated automatically, and weapons can be moved from the armory to the lift via electric carts without human assistance, improving safety and reducing crew requirements. Ordnancemen on deck can input projected ordinance needs into the automated control system, and the computer will automatically queue up the proper loads to the proper lifts for maximum efficiency and reduced deck travel times. In the unlikely event of malfunction, the system can be operated manually by ordinancemen to continue operations.

The port-side elevator can also be used to embark and deploy small boats. With the elevator at the flight deck position, cranes mounted to the port-side hull can be used to raise and lower boats and other cargo into the water. This feature was considered a priority to allow for the deployment of special operations troops by boat, and potentially to allow rescue submarines to be delivered by aircraft directly to a battlegroup and then be deployed without additional equipment. The cranes together are capable of handling up to 100 tonnes and can be operated at up to 20 knots. The two aft starboard-side elevators are designed to accept underway replenishment linkages.

One unique feature of the class is the addition of a second modular mission bay below the hangar deck. This space was previously occupied by the steam equipment, larger reactor footprint, and additional crew space in the previous class, but was freed up by the expanded hull and improved spacing efficiency. Equipped with two lifts to the main hangar deck, this space can be used as a supplementary hangar, storing lower-priority aircraft, large spares, and other equipment, or converted into a number of other uses, such as a barracks to house troops for amphibious operations, additional munitions space, command facilities for operations, and medical facilities for humanitarian operations. In normal operations, it can be used to clear the deck park to increase space for active operations. This space is located in the bow and measures approximately 75 meters in length, 8 meters in height, with a width varying between 30 and 25 meters.

Damage control

The magazines and reactor systems are protected by a double-layer 30 mm spaced armored box, designed to prevent penetration by splinters from bombs and missiles. The magazines, reactor, and fuel bunkers are additionally protected by 70 mm of kevlar armor to prevent spalling and other residual impact effects. All three are also equipped with a seawater automatic firefighting system, as well as an inert gas fire suppression system, which reacts automatically to detected breaches to prevent a potentially catastrophic detonation.

The main hangar bay is also equipped with four sets of large steel fire doors, capable of sealing the hangar into six compartments, as well as an additional set of six fire curtains for smaller conflagrations. The large elevator doors can be open or shut within 10 seconds, to either ventilate the space or remove oxygen sources for a fire and/or reduce radar returns. The lower modular space has two sets of fire doors and four sets of curtains, but no direct ventilation due to its low position in the hull.

Command and control

The Leptis Magna-class uses the Stele Integrated Combat Management System to control virtually all operations on the ship. The Stele hardware system uses modular Open Compute server racks connected with 100 Gbps standard fiber-optic taps, allowing for hardware to be replaced and upgraded at will without needing to replace the entire computer infrastructure. The fiber-optic cabling allows for longer cable runs with reduced signal degradation as well as increased bandwidth while also reducing EMP vulnerability.

Using standard commercial connectors and COTS modular hardware standards, processing units can be swapped out in minutes and the system can accommodate nearly any form of processing architecture, allowing purchasers to use indigenous components if desired. The Stele software itself is designed to be hardware-agnostic and scalable to incorporate future improvements, which with the existing power generation overhead can be significant in the coming decades.

The previous six radar systems used in the Hannibal Barca-class were replaced with only two units in the Leptis Magna-class: the RAN-34 dual-band search and tracking radar, and the RAD-40 L-band air control radar. The RAN-34 is an AESA radar operating on both the X- and S-bands for volume search and target acquisition, with an estimated range of some 400 kilometers and capable of tracking up to 300 airborne targets. It is mounted on the tall octagonal main mast, with four panels for each band providing continuous, full coverage with no moving parts. The RAN-34 is mounted lower and is designed to manage both arrival and departure air operations.

Stele at the ship level is designed to integrate all sensors and control systems to give the most complete picture possible to the crew and decision-makers in the loop. It can also recommend tactical responses based on detected attack profiles against the host ship, and take action autonomously if a detected attack is judged to give insufficient human reaction time.

The network aspects of Stele also allow it to both send and receive additional data from other ships and aircraft, both those operating a similar network and those operating a compatible interface. Thus, it is possible for a ship using Stele to engage a target it does not directly detect, so long as a node in the network has the proper targeting data. This means that the carrier's CIWS grid can be remotely linked to a potentially more powerful radar array on an escorting missile cruiser, or its torpedo defense system coordinated with the fleet to ensure maximum coverage.