It is said that the success of British encryption experts in cracking the Nazis' "unbreakable" Enigma cipher machine probably contributed more to the Allies' eventual victory than the more famous Manhattan Project that developed the atomic bomb.
Today China, the US and other major powers are racing to develop another game-changer in intelligence encryption - the first quantum supercomputer, which would become the ultimate code-breaker.
Quantum computers have so far existed mainly in the world of science fiction and research laboratories. But they hit the headlines recently after it was reported that the US National Security Agency had been building "a cryptologically useful quantum computer [in] room-sized metal boxes", according to documents leaked by Edward Snowden to The Washington Post.
The NSA regards itself as on a par with quantum computing labs in Europe in terms of progress, but a breakthrough soon remains unlikely, the documents said.
China is working on an ambitious project of its own and has built a new facility in Hefei , Anhui , in which to do it.
Thanks to such bizarre features of quantum physics as "superposition" and "entanglement", a quantum machine could, the theory goes, think in terms of "zero" and "one" at the same time. It would be therefore able to carry out millions of calculations simultaneously, while even the most powerful of today's computers chug along solving each task one after the other.
The possible uses of the quantum computer make it the holy grail of intelligence encryption. It could be used to break even the most secure codes used by banks, governments and militaries around the world.
While there is no sign that China is close to developing a practical, working model, it has pulled out all the stops to build the ultimate code-breaker.
At leading universities, state research institutes and the military, scientists have been given the green light - and, one would assume, ample resources - by the government to create the first quantum supercomputer.
Researchers working on projects from the generation of the strongest ever man-made magnetic field to building a "quantum chip" from diamonds have been told by officials to get the job done, regardless of how much it costs.
The Steady High Magnetic Field Experimental Facility, housed in a three-storey complex on the Hefei Science Island, could be activated this year to create the extreme environment needed to make quantum computing possible.
The facility was designed to generate and maintain a magnetic field at 45 Tesla, a feat listed by Guinness World Records as being achieved only by the National High Magnetic Field Laboratory in the US.
Once in operation, the new Hefei facility would likely exceed the 45 Tesla output.
Dr Chen Hongwei, a researcher at the Chinese Academy of Sciences' High Magnetic Field Laboratory and leader of the quantum computer project at the magnetic facility, said strong magnetic fields could overcome some of the biggest obstacles in quantum computing.
To function properly, a quantum computer would have to employ particles that had been given the state of superposition that allowed the information of "one" and "zero" to be carried simultaneously by each "qubit", or quantum bit, the unit of quantum information.
The more qubits that are used, the more powerful the computer would become.
The problem, Chen said, was that qubits were very fragile, and tended to remain very close to one another in a fuzzy cluster, making computing operations difficult, if not impossible.
"You can't do anything with a qubit if you can't even find one," he said. "However, under super-strong magnetic fields, the distance between qubits can be increased, making our jobs easier."
Experiments using smaller magnets at the facility have had encouraging results, Chen said. It was hoped that qubits would be "tempered" in magnetic fields of 45 Tesla or higher when the facility's most powerful magnet is commissioned this year.
"If qubits can be tamed this way, the first quantum computer may be born inside a magnet," Chen said.
The Hefei facility consists of an enormous magnet and a maze of pipelines and water tanks to cool the intense heat generated by its operation.
"However, if it turns out that quantum computing can be carried out only in extreme environments like super-strong magnetic fields, I am afraid the first quantum computer will be a big hill to climb," Chen said.
"Also, the magnet requires an enormous amount of energy to keep it working - so it would probably need its own dedicated power station as well."
Such restrictions obviously put quantum computing well beyond civilian use, he said.
To make a quantum computer as easily accessible as today's PCs, scientists would need to avoid such extreme environments. "A quantum computer that works in such an extreme environment has no commercial or personal use," he said. "But governments may want it for special purposes."
One major challenge for the Hefei experiment is maintaining the stability of the magnetic field at high operational intensity. The stronger the magnetic output, the more difficult it is to maintain a stable environment for quantum computing. One source of disturbance comes from the cooling system, the vibration of which might affect the delicate operation of the qubits.
The Hefei experiment is just part of the government's intensive effort to develop a quantum computer.
The National Natural Science Foundation of China, for instance, funded 90 quantumrelated projects last year.
Professor Wang Haohua, a physicist at Zhejiang University, who is trying to build a quantum computer with superconducting materials, said the central government was so eager - even desperate - to have one that scientists had been told to ignore non-technical constraints such as cost and size.
"The value of the quantum computer to the military and government is so great, its cost has never been considered," he said.
"Many Chinese scientists abroad, such as myself, have been attracted by the rapid technological development in China and are returning home.
"We hope to help China catch up with the West. It is not impossible that we may even win the race in the future."
In 2010, a team at the University of Science and Technology of China (USTC) surprised the world with a demonstration of quantum computing inside a diamond.
A nitrogen atom inside the diamond was used to perform quantum computing at room temperature.
Professor Hu Lei, a cryptologist at the State Key Laboratory of Information Security, said that no encryption method in existence today could resist an attack by a quantum computer, and that Chinese cryptologists were already preparing for the quantum age.
"Though it is difficult to build a defence without an enemy in sight, it will be too late to start if the first quantum computer appears on the horizon," he said.
"Quite a few research projects have been launched to develop quantum cryptology."
But professor Zhao Hongwu, a researcher with the CAS Institute of Physics on qubit storage materials and technology, said the first quantum computer could still be decades, perhaps even centuries, away.
He said China should adopt a long-term view.
"The government has invested in many approaches today because none of the present ones looks particularly promising," he said.
"It is very likely that more than 99 per cent of research will end up in failure. But the work must be done, or we will never know which method works."