A spy satellite beams a high-definition thermal image to the field command of the Jinan military region's cyberwarfare 'blue unit' via an encrypted downlink. A large enemy force of tanks, artillery and heavily armed troops has massed at the border, under camouflage to escape the notice of Chinese sentries. Within minutes, more than 300 blue unit computer specialists are at their posts. They find a 'back door' in the enemy's radio communications and infiltrate their military network. Drones and helicopters take off from a border airfield and strike the enemy's secret supply bases and convoys. The would-be attackers abandon their assault. The cyberwarfare scenario is just one of the various exercises involving military blue units, or cyberspace special forces, that have been described in recent years in PLA Daily, the English-language edition of the People's Liberation Army daily newspaper. The existence of these semi-independent units in all military regions was confirmed in May by the Defence Ministry. The units are co-ordinated by the Information Security Base under the control of the PLA's General Staff Department. Already, a large number of soldiers have been trained in hacking and defence skills. And, from the army, air force and navy to the strategic missile force, the blue units have developed their own tactics to deal with their perceived enemies, mainland military experts say. Strategically, the blue units apply in cyberspace Mao Zedong's doctrine of guerilla warfare - the concept of avoiding direct confrontation with big and powerful enemies such as the United States. Mao abandoned big cities when taking on the invading Japanese and anti-communist Nationalists. He established strongholds in less-developed rural areas and constantly hit the enemy's regular armies with small bands of guerillas. He also mobilised large peasant militias to fight powerful but less numerous enemies. It was a strategy that eventually proved successful. Decades later, that approach to warfare is guiding the PLA's operations in cyberspace, according to a 2006 paper by Dr Wan Dongsheng, a cyberwar specialist with the PLA's Electronic Engineering Institute. Wan says that any confrontation between China and the US in cyberspace today would have many similarities with those earlier wars. Again it would be a case of seemingly less-developed technology squaring off against a more advanced one, involving many people against a few. China might lose considerable ground in the early phase of war, but the guerilla strategy would consume the enemy and grind it down at enormous cost. China's guerilla attacks would avoid defence strongholds such as military command centres. Instead, it would target civilian sectors such as the power grid, financial system, international trade, transport and even hospitals to cause the greatest damage, given that more than 95 per cent of the US military's network is connected to the internet. Wan says a prolonged guerilla war in cyberspace would require the mobilisation of the people, and the military and government should plan for a total cyberwar, giving the country's hundreds of millions of internet users professional guidance, training and organisation. Bai Chenggang, a professor at Beihang University's School of Automation Science and Electrical Engineering, also sees the internet as an efficient - and cheap - way to train a vast number of people in 'network confrontation'. Trainees could receive practical demonstrations on cyberwarfare by video. Regular exams could assess their progress and performance. The PLA's strict media policy forbids active-duty officers from speaking to overseas media. But their articles in academic military journals offer a consistent picture on the development of cyberwarfare units on the mainland. Ren Xiaowei, a navy officer with the PLA's 91878 Unit based in Zhanjiang, Guangdong province, wrote in 2008 that the navy's cyberwarfare units were developing hardware and tactics for simultaneous attacks on different enemies. For example, a battle in the Taiwan Strait might involve the forces of many countries, each with their own communications systems and chains of command. The mainland's navy must be ready to infiltrate or suppress these different networks at the same time, a far more complex challenge than any that land or air forces would face, Ren wrote. Liu Chaoying, a researcher at the PLA Air Force's Radar Institute, wrote last year that the air force was studying how to infiltrate an enemy's communications network or launch an attack from airborne cyberwarfare units on long-distance bombers. Air force blue units would fly to regions where enemy radio activity was detected. They could either launch an infiltration or attack, or relay the information to supercomputers at the Information Security Base for analysis and decoding. So on their own, the guerilla cyberunits would not be enough. Dr Lu Sheng, a security expert and former IBM scientist, says the PLA's guerilla strategy might work in some areas of cyberwarfare where luck or intensive labour are important - for example, finding weakness in an enemy's military network. 'Sometimes, the more people you have, the greater your chance of finding a tiny hole in the enemy's defences,' he said. 'But whenever the work required big weapons such as supercomputers, small cyberunits would be helpless.' But China is also a world power on that score, having developed some of the world's most powerful supercomputers, such as the Tianhe series by the National University of Defence Technology. Still, some leaders are yet to be convinced to abandon tried-and-true methods. 'As far as I know, Chinese military leaders are very cautious about cybertechnology,' Lu said. 'Top secret military orders are still hand-written and delivered by messenger.'