Size Matters: Britain's Aircraft Carriers

"The aircraft carrier is truly amazing. I am amazed at the concept of the carrier, and the fact that it works. And it doesn't just work, it kicks butt.

-Lt. Barry W. Hull, VFA-81 Squadron, USS Saratoga, 1991

Why build big? It's a simple question asked frequently about the UK's two new Queen Elizabeth class aircraft carriers. Weighing in at just over 70,000 tonnes they are, by quite a long way, "the largest ships ever built for the Royal Navy". Many have leveled criticisms against them because of their size, claiming they are little more than a vast vanity project, that their size makes them unsuitable for a "medium power" such as Britain and that they reflect a yearning for a status on the world stage that is undeserved. What these criticisms ignore is that there are serious practical reasons why larger carriers are, in most circumstances, a significantly better investment when compared with smaller "pocket carriers" such as the Invincible class ships the UK operated from the late 70s through to 2014; when HMS Illustrious was decommissioned.

Efficiency:
Probably the key reason why larger carriers are significantly better than their smaller cousins is that they are a more efficient way of sustaining air operations from the sea. Generating the same effect with numerous smaller carriers, as some have suggested as a better course for the UK to follow, simply costs much more. The obvious consequence of this is that you get a force of smaller carriers that cannot deliver the same effect as fewer, larger, ships. The reason why this is the case can be neatly summed up with a single word: duplication. This is especially true of the manpower required to run two equivalent carrier forces, equal in "striking power", where the only difference is the size of the ships.  While the individual light carrier will undoubtedly have a smaller crew than an individual large carrier, you might need two or three smaller carriers to achieve the same number of sorties as a single, larger, ship and each still requires a range of highly trained crew members. To draw upon a real-world example: HMS Queen Elizabeth has a core crew of ~679, will carry and operate a tailored air group of 40 aircraft and can surge 110+ sorties a day. In comparison the 25,000t ITS Cavour has a core crew of ~451, an air group of around 20 aircraft and can surge approximately ~40 sorties a day. This means that, broadly speaking, in order to achieve the same effect as a single Queen Elizabeth you need approximately three Cavour-style light carriers on station, with manpower equivalent to double that of the larger ship. When considering the force structure necessary to ensure there are three small carriers available at all times for operations, taking the Royal Navy's current ratio of around 2 ships in maintenance for every 3 ships operationally available, you're looking at a fleet of five light carriers to achieve the same notional operational effect as a pair of Queen Elizabeths. Overall the model of smaller, more numerous, ships would require between 20 and 35% more manpower across the entire carrier force. At a time when the Royal Navy is hard-pressed to man its existing fleet a solution that involves adding up to a third more ship-side manpower to the carrier force is simply impractical and would add substantially to the force's through-life running cost.

As the ships get smaller their efficiency decreases markedly. Concepts for extremely small VTOL carriers, such as the one illustrated below, essentially amount to a reductio ad absurdum but nevertheless prove the point that greater numbers of smaller carriers become exponentially more expensive to produce the same effect in terms of available aircraft and sortie generation. Furthermore, there is also needless duplication in terms of aircraft maintainers with small carriers. It takes a similar number of trained engineers to maintain a small number of aircraft operated from a small carrier as it does to maintain a larger number on a larger carrier, once again duplication of functions across multiple platforms leads to greater manpower needs, reduced efficiency and increased costs across the entire fleet. The cost of the ship per aircraft carried also increases significantly as the platform becomes smaller. Taking into account that the RN, when presented with the opportunity to replace their old carriers, was instructed by the government that no more than two new ships would be procured it then becomes clear that two larger ships were the clear and preferable choice.

Concepts were produced for very small carriers, this modification of the "Type 43" destroyer examined the possibility of operating a pair of STOVL Sea Harriers from escorts. Image courtesy of D.K Brown & Moore's "Rebuilding the Royal Navy"

Sustained Operations:
The next major limitation on many smaller carrier designs is their capacity to conduct sustained air operations. This is due to a number of factors, but principally comes down to aircrew endurance, aircraft maintenance and supply limitations. As you can well imagine it is easier for a carrier with a larger air wing to conduct more sorties in a short-term high-intensity surge effort, however, their advantage becomes even more obvious when looking at sustaining a more modest number of sorties over a longer period of time. Facilities for planning and briefing multiple air operations are also more limited aboard smaller ships. Light carriers with smaller air groups place greater demands on a smaller pool of pilots and other air crew when sustaining operations over time, or compromise by reducing the number of sorties flown. Similarly, working a smaller number of aircraft harder to sustain operations leads to greater wear on individual aircraft, increasing the risk that they end up out of action without an available replacement. For example, during NATO bombing operations in 1995 Britain's "pocket carrier" HMS Invincible was struggling to sustain eight sorties a day with her eight embarked Sea Harrier FA.2s (and both Sea Harrier models had a reputation for being robust and reliable aircraft). A larger carrier with more aircraft embarked can better afford technical problems which prevent some aircraft from operating, because each individual aircraft's availability is less important when a large pool is available to draw from.

Logistics are also another crucial advantage of larger carriers, as greater space for fuel and stores makes them less reliant on frequent resupply operations which take time and prevent flying operations. The Invincible class were (despite some mid-life improvements to the quantity of ammunition they could store in their magazines) always tied very closely to their attendant fuel and stores ships. By comparison the Queen Elizabeth design can hold fuel and stores for around ~400 "strike" sorties, sufficient for five days of very high-intensity operations (defined as a first-day Surge of 110 sorties, followed by 72 sorties a day for four days) before needing to come "off station" in order to resupply fuel and ammunition. Alternatively, a more relaxed tempo could obviously be sustained over a longer period of time. Considering that the Libya air policing mission only required 36 sorties per day to enforce, after the first 11 days spent degrading Libya's air defences, QE could sustain a similar lower tempo operation without resupply for 11 days.

The Invincible class light carriers struggled to sustain air operations for an extended duration without reduced sortie rates and heavy dependence on attendant logistics ships.

Eggs and Baskets:

There is a superficially appealing argument that reliance on a smaller number of larger ships amounts to "placing all of one's eggs into a few very expensive baskets". While this may sound like an enlightened nugget of wisdom on the surface, dig a little deeper and you find that it's a flawed argument. Firstly, "hardening" a carrier force by using a greater number of smaller platforms only works if you have the escort warships to form multiple carrier groups. Without a sufficient number of these ships, which form a vital part of the carrier's layered defences, the available escorts will either be too thinly spread to be effective, or the carriers will have to be concentrated within the protected zone afforded by the available escorts. The first approach risks spreading available forces too thinly, dispersing them into vulnerable "penny packets", while the second only provides marginal benefits over having a single larger ship at the centre of the carrier group. Effective dispersal of the carrier force would multiply the number of effective escort groups required, something that is beyond the current capabilities of the Royal Navy. Secondly, a more dispersed carrier force would also require the dispersal of logistics support ships. As presently planned the UK carrier group will be supported by a large fleet tanker and solid stores ship, in comparison multiple smaller carriers would each require a roughly equivalent number of support ships (and would be more dependent on them, as their own fuel and magazine space would be more limited). If, broadly speaking, three smaller carriers are necessary to replicate the capability of a single larger carrier then the overall force will require something like triple the number of logistics ships and escorts; if the carriers are operated separately in order to take advantage of the dispersed approach. Even then, each group centered on a light carrier will have fewer aircraft available to contribute to the outer ring of its layered defense. This means that Combat Air Patrol (CAP) operations, designed to keep hostile aircraft away from the carrier group, would require a greater portion of the air group's effort and leave fewer aircraft available for offensive operations. What this means in practice is that the smaller carrier would be expending so much effort protecting itself and its escort group that its "punch" would end up being anemic.

The alternative approach to effective dispersal is concentrating multiple smaller carriers within the same group. This does have the clear benefits of not requiring nearly as many additional escorts and also limits the need to duplicate replenishment ships. The group's "punch" is also greater, due to the larger number of available aircraft for all duties, albeit spread between a number of ships rather than concentrated on one. Indeed, the concentrated approach was taken by the commander of the British naval task force that fought the 1982 Falklands War; with HMS Hermes and HMS Invincible operating together throughout most of the conflict. However, it is important to note that this means of employing smaller carriers sacrifices the key benefits of effective dispersal: the increased difficulty of locating the entire carrier force for the enemy, the ability to deploy the dispersed groups to different areas and the increased "coverage" this can provide (especially for anti-submarine operations). It is a fundamental principle of military operations that force be concentrated in order to achieve decisive effects, while a dispersed force may allow individual platforms to survive it is far less useful for striking hard blows against an adversary.

Operating a dispersed force of smaller carriers requires significantly more escorts and logistics ships and must still be concentrated in order to achieve decisive military effects in most circumstances.

Conclusions:
I began this piece with a simple question: "why build big?" and the answer is now clear. When discussing aircraft carriers, from a purely functional perspective, size matters. Setting aside the soft power and symbolic implications of operating large carriers entirely, they're simply better from a pragmatic position. Smaller numbers of larger carriers are more efficient in terms of manpower, cost per aircraft carried and supporting ships than larger numbers of smaller carriers. For the Royal Navy, told that they would only get two ships to replace the remaining Invincible class carriers, the decision was clear and they chose to build two large, efficient and effective ships. This was, for all of the reasons discussed, absolutely the right decision for the UK. The new Queen Elizabeth class, once fully worked up, will be capable of conducting extremely intensive "short and sharp" air operations before exhausting her own supplies of fuel and ammunition or sustaining a lower tempo of operation for a significant time. They will be able to bring a decisive level of force to most engagements, instead of the small "penny packets" of aircraft aboard light carriers. Along with a properly constituted escort group the larger carrier is also capable of simultaneously defending itself and conducting meaningful strike operations when necessary. For those who claim that the UK's large carriers are simple a vanity project I would respond by stating that deliberately pursuing a more expensive and less effective solution, in the form of smaller carriers, because of a perception that they "better suit Britain's position in the world" is not only vain but unnecessarily introspective and downright foolish. When it comes to carriers, the UK has absolutely made the right choice. Bigger is better.