I'm mostly interested in medieval applications, but other areas would also be good.
Edit: I mean the tactics and strategy described rather than the use of the text itself.
I was almost tempted by the incivility of your response not to answer (I mean equating a Saiyan to Vegetius is a bit of an insult to Vegeta) but decided to do it anyway. My answer will focus not on medieval but on the Qing period in China (1644-1911).
Let's start with a quotation – those are always fun. My favourite quote from the Kangxi Emperor (reigned 1661-1722) is coincidentally one of my favourite pieces of commentary on China's military classics, and comes from a 1710 memorial:
I have read the seven military classics in their entirety and find them a real mishmash, to the point that they cannot possibly be brought into accord with righteousness. This talk of “attacking with fire” and “water wars” is all nonsense. If one were to follow these directions there would be absolutely no method for gaining victory. And then there is the talk of secret allies, power over the elements, prognostication and so on. This serves only to pervert the minds of small men. Since over the years the three feudatories have been pacified, Taiwan has been taken, and Mongolia has been pacified and ordered, I have dealt with a very large number of military matters. I have personally led punitive military campaigns and I deeply understand the way of generalship. How can we wholly depend on what is said in the seven books?... Anyway, the idea that “The benevolent man can not be defeated” is the way of the king. Using schemes, deceit and baseless talk is not as good as the way of the king, which means refusing to do battle only to see the enemy’s troops defeat themselves. The two words “way” and “king” represent the most ingenious military techniques. Since ancient times bellicosity has been a hideous thing. Those who excel in warfare all put off the use of war until, compelled by circumstances, they lose all choice in the matter. Since ancient times bellicosity has been a hideous thing. Those who excel in warfare all put off the use of war until, compelled by circumstances, they lose all choice in the matter. In the past when Wu Sangui rebelled, Jiangnan and Huizhou lost one xian to rebellion. A general named Echy led a punitive force there. One man offered advice to the rebels, saying, “Manchu soldiers can’t fight on foot. If you order people to lure them into the rice fields, you’ll definitely defeat them.” Ignorant that Manchu soldiers are tough, brave, and aggressive, those who wished to lure in the Manchus had not even reached the rice fields before they had all been slaughtered. He who had offered the advice was killed by my troops. Those who employ the seven military classics are all like that man. ^1
The 'seven military classics' here include the Art of War, along with several other texts, none published later than the late 11th Century.^2 For context, Kangxi was at this time planning to reform the Qing military examinations, and later on in this passage he recommends combining military books with the Analects and Mencius – standard works of civil philosophy – to form examination questions.
It is possible to read this passage several different ways, and although the conclusions are unambiguous, the reasons are less so. One can see it as Kangxi taking a reasoned stance in rubbishing archaic and arcane practices – Jonathan Spence uses the first few sentences of it in Emperor of China implicitly to this end.^3 However, my reading of the quote leans more towards the idea that Kangxi was affirming the martial virtues of Manchus such as himself, who had gained China by conquest in the 1640s. In Kangxi's view, the Han Chinese were 'no worse' intellectually than the Manchus, but far more lacking in military prowess, and he would insist that the Manchus maintain their militaristic fe doro ('old ways'). To me, this quote is Kangxi basically asserting that the Manchus had nothing to learn from the Chinese, whom they had so easily overrun. Whichever way you look at it, though, there was a clear sense from the emperor that he would not allow military practice to be dominated by centuries-old Han Chinese theory. Kangxi was, however, bucking the trend, and this idea did not last much longer than his death. His grandson, the Qianlong Emperor (reigned 1736-1796/9) reversed the reforms in the late 1750s.^1
Was Kangxi right in this regard? Possibly, possibly not. Military theory is messy business and just about any point sees disagreement. Yet in the years preceding Kangxi's accession – and in a couple of cases, after it – precepts of Sunzi – albeit rather obvious ones – gave Chinese generals great success against various foes, including Europeans. Before the battle of Liaoluo Bay in 1633, Ming admiral Zheng Zhilong – whose use of fireships would severely damage the Dutch fleet – explained that his plan was based on Sunzi's insistence upon the importance of speed, quoting chapter XI of the Art of War: '兵之情主速' – Speed is the essence of the warrior. His son, Zheng Chenggong (also known as Koxinga) similarly used a stratagem of Sunzi to severely maul a Manchu army in 1652: 絕水必遠水，客絕水而來，勿迎于水內，令半濟而擊之利 – When an invading force crosses a river in its onward march, do not advance to meet it in mid-stream. It will be best to let half the army get across, and then deliver your attack. Pithy maxims like 亂而取之 – feign weakness to lure the enemy – or 夫兵形象水，水之形，避高而趨下：兵之形，避實而擊虛；水因地而制流，兵因敵而制勝。 – Military tactics are like unto water; for water in its natural course runs away from high places and hastens downwards. So in war, the way is to avoid what is strong and to strike at what is weak – became almost mantra-like, and heavily informed Koxinga's tactical thinking when dealing with the protracted siege of the trace italienne fort of Zeelandia in 1661-2.^4 ^5
It is quite interesting to contrast the Kangxi Emperor's perspective with that of Hunanese bureaucrat-turned-general Zeng Guofan, who was tasked in 1853 with raising an army to fight the Taiping Heavenly Kingdom. Zeng's army would be the one to deal the final blow to Nanjing, yet in early 1861 – half a year before his crucial victory at Anqing – Zeng, convinced of his imminent capture and execution, wrote a will in which he noted that 'Warfare calls for extremity, but I am too balanced. It calls for deception, and I am too direct. How could I possibly manage against these monstrous rebels?'^6 The idea of warfare as largely a realm of deception – in essence, war of information – is again heavily informed by Sunzi. Yet Zeng Guofan, the sort of person whom Kangxi probably would have favoured given his classical civil learning combined with hard-won military experience, did not share with Kangxi the same view of the crossover between the 文 (civil) and 武 (military) spheres, or at least the idea that people suited to one were also suited to the other.
Further down the line, however, Sunzi was arguably rather sidelined. One critic at the 1935 Zunyi Conference accused Mao Zedong of having derived all of his military capabilities from the Romance of the Three Kingdoms and the Art of War, but Mao admitted later on that at the time, he hadn't even read the latter. Like Kangxi, Mao was much more of a Clausewitzian, for whom politics and war were inextricable,^7 in contrast with Sunzi's famous line denouncing state interference in military matters: 將能而君不御者勝 – *He will win who has military capacity and is not interfered with by the sovereign.*^5
Sources, Notes and References:
Do we mean The Art of War by Sun Tzu – and therefore China – or more general ancient military works like those of Frontinus or Vegetius?