HMS Queen Elizabeth – built to survive
In a previous article, we looked at the active layers of protection that will surround HMS Queen Elizabeth when she is required to sail into harm’s way. In this piece, we will look at some of the passive design features that would help preserve the ship if the worst happened and she was damaged.
The Royal Navy has considerable accumulated experience in how to design aircraft carriers that can withstand damage, many of the lessons were learned the hard way during brutal actions during WWII. In the 1930s the RN decided that all its carriers would have armoured flight decks and protected hangars. This additional weight required greater structural support that constrained hangar size and aircraft numbers. Unarmoured US carriers could embark more aircraft but suffered grievous damage when hit, while RN carriers were able to quickly return to operations, within hours of bomb or kamikaze strikes. Despite the benefits of toughened flight decks, WWII conclusively demonstrated the days of heavy armour were over. Even the most well-protected battleships ever built, the Japanese Yamato class succumbed air-launched bombs and torpedoes.
Post-war carrier design still favoured armoured flight decks but by the by the time the Invincible class (CVS) were designed in the 1970s, naval architects had long since abandoned serious structural defence against the power of modern explosives carried by torpedoes and guided weapons. Today’s warships have many damage control features but are of relatively light construction and have dispensed with armour in favour of self-defence weapons, decoys, electronic countermeasures and stealth.
In 2000 the USS Cole was badly damaged and 17 sailors killed in Aden harbour by a terrorist attack using small boat packed with explosives. This event was a wake-up call to warship designers about the new asymmetric threat in harbours and confined waters. The incident coincided with the early design phase of CVF (that became the Queen Elizabeth Class aircraft carriers). It would be an embarrassing disaster, should the ship be disabled by a terrorist with simple or home-made weapons costing a few hundred dollars. Greater protection from RPGs, suicide craft and unmanned boats or drones became an urgent consideration.
In 2002 QinetiQ were contracted to assess how damage-resistant the early CVF concepts would prove in a wide range of scenarios, ranging from an RPG strike to multiple torpedo hits. QinetiQ has developed a sophisticated software toolset called Survive® based on more than 50 years of full-scale trials and experimental data. Computer models of vessels can be subjected to virtual damage and evolved algorithms can calculate the effects on structures. QinetiQ’s Marine Survivability Services has a team of specialists with extensive knowledge of ship and submarine vulnerability. The Survive® toolset continues to be refined and has been used in the design of all major RN vessels in the 21st Century. QinetiQ also has a full-scale shock-testing facility in Rosyth used for evaluating naval and commercial marine equipment. A two tonne Shock Table (2TMC) and Deck Shock Machine (DMC) has recently been recommissioned.
In 2002 the leading candidate for CVF was the Thales Alpha design that incorporated self-defence weapons including Aster missiles and many other desirable, but expensive features. Side armour and blast resistant bulkheads were added to the Alpha design as the result of the QinetiQ studies. Unfortunately, the Alpha was a casualty of the first of the CVF cost-saving rounds. In late 2003 the 65,000 tonne, 9-deck Delta concept was adopted, being 20m shorter and more affordable than the Alpha, it was the basis of the QEC we know today. Much of the protection incorporated in the Alpha design did not feature in the Delta, although a basic level may have been retained.
The details and location of any armoured or protected parts of the ship are rightly classified, it would obviously be useful to any potential adversary to know the stronger and weaker points of the vessel. The likely areas that would be the priority for additional protection would be the operations room, weapon magazines and steering gear, all of which are deep in the ship. The only publicly acknowledged armour on the QEC is the armoured glass fitted to the Flying Control office (Flyco) which is made to withstand the full impact of a rotating Chinook helicopter rotor blade.
Armour protection for warships is available in 3 main types of material. 1.) Traditional warship armour made of toughened steel plate which is the cheapest but heaviest solution. 2.) Ceramic composites, a well-known example is the Chobham armour used for protecting Challenger II main battle tanks. 3.) Synthetic composites such as Kevlar which is very strong, about 20% of the weight of steel and very expensive. It is known that the US Navy’s later Nimitz class aircraft carriers employ two-and-a-half inches of Kevlar armour in places and the Arleigh Burke class destroyers vital areas are protected by 70 tons of Kevlar sandwiched between two layers of steel.
More important than any armour protection is the overall resilience of the ship design. Despite pressure to cuts costs, we can be thankful that QEC was built to very high damage control standards. This kind of protection would be expensive or near impossible to retrofit at a later date. Further QinetiQ input into the Delta design informed measures to mitigate the effects of blast, fragmentation, shock, whipping, fire and flooding. It is the goal of all good warship design, to build a vessel that can survive some hits or near misses without catastrophic damage and is able to continue to float, move and fight.
Float, move, fight
The QEC are divided into 3 ‘citadels’ with independent power, fire mains, ventilation and services which should remain functioning should one of the other citadels be damaged. There are multiple redundancies allowing systems to be cross-connected in the event of failure. As is usual in warship design, watertight doors and hatches are fitted throughout the ship. Should a few compartments be flooded, provided they are sealed, the ship can still float, the first element of survival.
The CVF is the first RN warship to be constructed to Lloyds Register Naval Ship Rules. This is a development of the safety certification system used for commercial shipping and sets standards for hull construction, propulsion and machinery, electrical power generation and distribution, automation, alarms and safety systems. HMS Queen Elizabeth was officially certified as conforming to these rules in a modest ceremony on August 7th 2018. However, the ship exceeds these standards in many areas. Rear Admiral Bob Love, CVF IPT team leader, stated in 2007 that “Specific naval and defence standards (DEF STAN) have also been retained in other areas where a commercial equivalent is not appropriate such as the magazines. Remember that the size of the vessel alone does give a degree of protection and this has allowed us to make pragmatic adjustments to the design.”
The QEC has duplicated main and secondary machinery in two well-separated complexes with independent uptakes and downtakes in the two islands. From a propulsion perspective, the QEC is like two ships. If the forward system is damaged, the after section will keep going and vice-versa, which should ensure the ship can move, although probably at a reduced speed. The two MT-30 Gas turbines and alternators housed in the sponsons below each of the islands are relatively vulnerable but are well separated at least. Even if both were damaged the four diesel generator sets in the bottom of the ship ensure she would continue to move.
The hangar is a very large space that will often be occupied by fuelled and armed aircraft, always a vulnerable aspect of any aircraft carrier. In the QEC the hangar is relatively well protected from penetration, at least by light weapons, almost surrounded two compartments deep on all sides and separated from the flight deck by a full-height gallery deck. The hangar is designed to contain fires, fireproof shutters can divide the space into 3 sections which can quickly be drenched in foam or water.
The twin island design also offers a duplication of conning position and aircraft control. Should one island be damaged, command can still be exercised from the other, an almost unique feature of the QEC that could help keep her in the fight.
The USS Cole survived partly because the CO had ordered all watertight compartments shut as a matter of routine when entering harbours. HMS Glamorgan (Exocet strike – 1982), HMS Southampton (collision – 1988) and HMS Nottingham (grounding – 2002) all survived very serious damage because of crews well rehearsed in damage control. However well constructed a warship maybe, a critical factor in survival is the training and efficiency of the ship’s company. The RN is renowned as a world leader in preparing sailors to mount effective damage control actions.
The final element is passive protection is stealth. The QEC are not true stealth ships but there are some measures to reduce signatures (radar, acoustic and heat). This makes them harder to detect and improves the performance of their own passive soft kill countermeasures and off-board decoys. The conventional main hull form is not optimised for stealth but the side sponsons that run most of the ship’s length, the catwalks, ski ramp and both islands have angled sides to reduce radar reflections. Without aircraft or vehicles on deck, the 65,000 tonne QEC is said to have a radar return typical of a very much smaller vessel.
In spite of the perceived vulnerability of aircraft carriers, they are surprisingly hard to sink, even if you can find them. In all the conflicts since WWII, not a single carrier has been successfully attacked (While countless airbases have been put out of action or over-run). New images of the decommissioned super carrier USS America being sunk as a live-fire test and evaluation platform in 2005 have emerged recently. Details are sketchy but she proved a tough customer. It took four weeks of being subject to explosions above and below the waterline before she finally disappeared beneath the waves.
This cursory assessment of a complex subject, using only public domain sources reveals the QEC, while not unsinkable, are resilient platforms and that have been constructed with a good balance between cost with survivability.