In his last column, my colleague Mark Steyn remarked that “the single greatest force for ending slavery around the world was the Royal Navy.” True enough, and a salutary, if melancholy, reminder of past glories. While a new threat to enslave the free world emerges in the Orient, Britannia not only does not rule the waves but has scrapped or mothballed so many warships that she is now weaker at sea than her old French rival.

British naval supremacy, which endured for more than two centuries until the torch passed to America, was a powerful force for freedom. But it came at a high price. The royal navy had zero tolerance, not only of tyranny and piracy, but of failure, and it treated officers or men who shirked their duty ruthlessly.

This ruthlessness made a lasting impression on friend and foe. We have just commemorated the case of Admiral John Byng, responsible for one of the royal navy’s rare reverses against the French. In 1756, sent to relieve a besieged British fort on the Mediterranean island of Minorca, Byng found himself outnumbered and he merely skirmished with the French. He then returned to Gibraltar, having failed in his mission. Minorca fell soon afterward.

Poor Byng was an early victim of adverse press spin. The French commander, Admiral Galissonnière, got his version of events into the public domain first, painting what was really an inconclusive engagement as a great French victory. Byng’s dispatch arrived too late. Public opinion was unforgiving, and his version was edited by the admiralty to put his conduct in a poor light.

Why? The British government, under its prime minister, William Pitt the Elder, was embarrassed by its own incompetence. It had failed to reinforce Minorca, which was commanded by a bedridden octogenarian who had allowed many of his officers to go on leave. The Pitt administration also had refused to give Byng enough ships, as he had requested. It decided, nevertheless, to make the admiral a scapegoat.

On his return to England, Byng was arrested and court-martialed. Confident of his innocence, he was indeed acquitted of the charge of cowardice. But he was found guilty of dereliction of duty. Two of the vice admirals on the panel of judges refused to sign the judgment, for which the only sentence was death.

All attempts to intercede on Byng’s behalf failed. There was even an appeal for clemency from one of Byng’s opponents at Minorca. The Duc de Richelieu, a marshal of France, sent a letter drafted by an acquaintance of Byng: Voltaire, then Europe’s most celebrated man of letters. But King George III and his prime minister were implacable: There would be no pardon. On March 14, 1757, exactly 250 years ago, Byng was shot by firing squad on the quarterdeck of his own flagship, the Monarch. The image of the execution, engraved and reproduced by the thousand, went round the world.

Voltaire, however, took a posthumous revenge for what he saw as judicial murder by immortalizing the incident in his most famous work, the satirical novel “Candide.” Arriving at Portsmouth from France, the eponymous hero happens to witness the execution. Shocked, Candide is told that “in this country it is considered a good thing to kill an admiral from time to time so as to encourage the others.”

Though Voltaire intended his catchphrase “pour encourager les autres” to be ironical, the fact remains that though the British lost the battle, they won the war. Minorca was one of the opening shots in the Seven Years’ War, perhaps the first truly global conflict, by the end of which the French had been driven out of India and Canada — thanks to the royal navy.

Two and a half centuries later, the Byng family is still angry. They want to know why, when World War I deserters are granted posthumous pardons, their ancestor remains in disgrace. To which the only answer is that of the Greek poet Agathon: “Even a god cannot change the past.”

Actually, Byng did not die in vain. Making an example of him did encourage British naval officers, because they knew that in the event of a court-martial, they would not be saved by their social connections. The royal navy has never needed to shoot another admiral to encourage the others; one was enough.

It is hard to be quite so sanguine about the effect on morale of courts-martial today arising from Iraq and Afghanistan. One of these cases, in which six army officers were cleared of killing an Iraqi terrorist suspect, ended last week after a three-year investigation costing some $40 million. The case should never have come to court, and it has damaged the reputation of the driving force behind it, the government’s senior law officer, Attorney General Lord Goldsmith.

Rather than shooting our officers to encourage the others, we punish them not for dereliction of duty but for doing it too zealously. That is not only unjust, but also self-defeating. Victory in war demands that officers do things — sometimes terrible things — that are above and beyond the call of duty. We need heroes, not scapegoats.