Does anybody still need aircraft carriers?

A major piece of Britain's new one has arrived at a dockyard, China is testing one, but 100 years after the concept was invented, does anybody still need aircraft carriers?

They are floating airfields that can deploy a nation's military might across the world's oceans.

In May 1912, the first plane took off from a moving warship, HMS Hibernia, temporarily adapted for the purpose. The idea of dedicated floating platforms had been mooted in 1909, but it wasn't until 1918 that HMS Argus became the first proper carrier.

Today, ownership of a carrier for fixed-wing aircraft admits a nation to an elite club, but the US has more than everyone else in the world put together.

The UK is currently not a member, but this month has seen a significant milestone on the country's journey to retaking its place.

Part of the hull of Queen Elizabeth has arrived at Rosyth where it is to enter the dry dock for the rest of the ship's construction. The ship, which left BAE Systems' Portsmouth yard, is due to be finished in 2017 and will be followed by sister ship Prince of Wales.

The Ministry of Defence says the ships and jets will cost £7bn, leading some newspaper columnists to argue that they are both an unnecessary expense and no longer strategically necessary for the UK.

For the Guardian's Simon Jenkins it is the "greatest waste of public money" of any government programme. The Times's Matthew Parris argued that the action in Libya had not shown the need for a UK carrier.

There have been sceptics for some time. In 1981, David Howarth wrote in Famous Sea Battles that "the only practical value of carriers in the future will be in simply existing, not in fighting". To use them in anger would be to trigger a nuclear war, he argued.

But just a year later, the UK's carriers ensured that the Falkland Islands were regained.

Different nations take different approaches to carriers. The US owns 11, or 20 if plane-carrying amphibious assault ships are counted.

Its 10 Nimitz class carriers are floating cities - the size of four football pitches - each housing 5,000 crew and 80 strike jets.

By contrast, Spain and Italy have miniature carriers with around a dozen planes, while China has only one ex-Soviet model, preferring to put its defence budget into missile technology.

After the US, France has the only serious naval aviation, according to IHS Jane's Fighting Ships.

Thailand has a very small carrier, which is not thought to have launched aircraft for some years. India is using the UK's former HMS Hermes and an ex-Russian carrier, and Brazil's is an ex-French vessel.

But does any country need aircraft carriers?

The US doesn't need so many, says Prof Andrew Lambert, a naval historian at King's College London.

But for the Americans it is about projecting power around the globe. And they see the aircraft carrier as the best equipment for their global role, Lambert says.

The logic for carriers is very simple. It allows a nation to take air power around the globe without having to worry about countries in between who might refuse the use of ground bases or airspace.

Bosnia was such a case, says former Royal Marine Major-General Julian Thompson.

"The Italians said you aren't going to fly from our airfields or over Italy." And he points out that the only enemy planes shot down by British aircraft since WWII have been by the Fleet Air Arm based on carriers.

But have things changed in the age of the nuclear submarine, precision missiles and the unmanned drone?

Unlike "pointless" frigates, carriers are still as relevant as ever, says Lewis Page, a former naval officer and author of Lions, Donkeys and Dinosaurs: Waste and Blundering in the Military. The drone might be all the rage but you still need somewhere to launch it from.

Nuclear submarines are "excellent" at many things. Their Tomahawk cruise missiles flew hundreds of miles to knock out Colonel Gaddafi's air force.

"But a submarine can't tell you where the targets are. And they can't be easily rearmed apart from at a naval base."