After the July 3 operation, Darlan immediately ordered the French fleet to attack British naval ships wherever possible. However, Pétain and Foreign Minister Paul Baudouin overruled Darlan’s order the next day. The compromise was a token, ineffective French air attack against the British base at Gibraltar. “The attack on our fleet is one thing, war is another,” Baudouin noted.

Churchill was greeted as a hero by the British parliament when he explained his actions; he took his seat with tears flowing down his cheeks.

Hitler told Italy’s Foreign Minister Galeazzo Ciano that the British attack was an act of madness that served German and Italian interests by sowing dissension between the recent allies. Germany subsequently permitted France to maintain its fleet armed rather than demobilized, as had been stipulated by the armistice. The British attack and the French hostile response strengthened Hitler’s view that he should not parcel out French North Africa to Mussolini and Franco.

MILITARILY, THE attacks were a mixed success. On the one hand, the British neutralized about half the French fleet and suffered no significant losses. On the other, only two of the four capital ships that Churchill most feared were put out of service. The Dunkerque was able to sail to Toulon within two years. Thus, the forecasts of Britain’s naval officers, opposed to the operation, had been overly pessimistic about possible British losses, but quite accurate about the limited damage to the capital ships.

Britain would also pay a price in the French Empire, as British skeptics had warned. French colonial forces defeated de Gaulle’s Free French Forces at Dakar in September 1940, cooperated with the Germans in Syria in the summer of 1941 and initially resisted allied forces in Morocco in November 1942. Recruitment for the Free French movement plummeted. None of these negative developments, however, were major setbacks.

A bitter Darlan had the last word. When the Germans tried to seize the fleet in Toulon in November 1942 in response to the allied invasion of Morocco, Darlan ordered the fleet to sail to North Africa. Instead, the local commander scuttled sixty-one ships. Darlan sent a letter to Churchill within days:

“Prime Minister you said to me ‘I hope you will never surrender the fleet.’ I replied, ‘There is no question of doing so.’ It seems to me you did not believe my word. The destruction of the fleet at Toulon has just proved that I was right.”

Churchill was right about the operation’s impact on global public opinion. Roosevelt’s aide, Harry Hopkins, told Britain’s ambassador in Washington, Sir John Colville, that the British attack convinced FDR that Britain was in the war for good. The attack therefore may have contributed to his decision to provide the UK with destroyers in September 1940. It also probably helped to convince Yugoslavia and Greece to resist Germany and Turkey, and Spain to remain neutral.

Thus, the British attack must be evaluated on two levels. In light of future events, the operation was a tragic mistake. Darlan was true to his word—though it had been a near-run thing with the German forces almost taking control of the ships at Toulon in November 1942. Moreover, the Battle of Britain several months after the Mers attack would have provided ample proof to the world that the British were serious about fighting on. Churchill could not have foreseen these events in July; his decision, therefore, was understandable.

Did Churchill make a mistake in encouraging the French fleet to join the British fleet? If the French had done so, would the Germans have taken Morocco and Algeria, thereby preventing or complicating the 1942 invasion? According to military historian Douglas Porch, this would have been highly unlikely. In 1940, Germany’s army had been stretched to its limits by the invasion of France. Neither Mussolini nor Franco wanted Germany to move into their backyards; by 1941, Berlin had turned its sights on the Soviet Union.

CHURCHILL’S ATTACKS against the French fleet offer four policy lessons. First, Operation Catapult suggests that, at times, leaders must consider using military power against friendly nations. Within three weeks of the armistice, Churchill was browbeating his naval officials into attacking their former ally. Perhaps he reminded them of the British naval attacks against the Danish fleet during the Napoleonic wars to prevent it from coming under the control of Napoleon and Russia.

The United States has engaged in military actions against friendly countries, if less dramatically. President Richard Nixon considered using military force in the 1973 Arab-Israeli war against Israel for all practical purposes. Initially, America supplied Israel with arms and munitions to stave off defeat, but then prepared plans to interpose American military forces to prevent Israel from crushing the Egyptian Third Army east of the Suez Canal, according to declassified Nixon-Kissinger telephone conversations.

Moreover, when the Falklands War broke out in 1982, Washington had to choose between its traditional British ally and Argentina, with whom it was working closely in Central America against Marxist guerrilla movements. It sided against Buenos Aires by providing extensive logistical support to the British, albeit clandestinely. There was a serious divide in the Reagan administration between UN ambassador Jeane J. Kirkpatrick, who favored the Argentines, and Defense Secretary Caspar Weinberger, who favored the British. The special relationship prevailed, in a minor recapitulation of America’s aid to an embattled Great Britain at the outset of World War II. The staunchly Anglophile Weinberger explained that “the U.S. action” was predicated “not on the fear that our ally would be defeated, but a fear that aggression would succeed and a resolve that the very strong, decisive and admirable action that Britain was taking should not go unrewarded.” Writing in the National Interest in the Winter 1989/90 issue, Kirkpatrick observed, “I desire also to make clear that I utterly disapprove of force as a means to settle disputes in general, and so disapproved of the use of force by Argentina in particular. I also regretted the British decision to go to war to settle the dispute.”

Could similar events happen in the future? Quick regime reversals such as in 1940 are always possible. Imagine if nuclear proliferation were to spread in the Middle East in the wake of a nuclear Iran over the coming decades. If an unfriendly regime were to replace a friendly one, as the Muslim Brotherhood did in Egypt in 2013, then Washington might issue an ultimatum to turn over the nuclear inventory or face attack. Furthermore, Washington should at a minimum develop arms that can be disabled where possible if they are captured by enemy forces, as happened recently with ISIS capturing U.S. arms from the Iraqi Army.

One could imagine America withholding some forms of military support to force Taiwan to walk back from a declaration of independence in order to prevent a larger clash between Beijing and Washington. The United States could, for example, refuse to help the Taiwanese fend off Chinese cyber attacks or to provide information for key American weapons systems until Taipei backed down from an independence declaration. And just as Nixon considered doing in 1973, U.S. naval forces might also be interposed between the mainland and Taiwan.

Second, military planning must take into account scenarios that are unlikely but not impossible and that have extremely high stakes. The collapse of France and the subsequent British naval attack at Mers el-Kebir dictates that the unexpected, even the astounding, must be taken into consideration in war planning. In early May 1940, British officials understandably could not conceive of a rapid and overwhelming German victory on land that would leave the French fleet intact. Within six weeks, they were faced with just such a situation.

Today, unlikely but fathomable military scenarios focus on biological or nuclear weapons. What if, for example, a ruthless dictator with an inventory of ballistic missiles with nuclear weapons commanded his forces from a deep underground urban bunker? The Obama administration should be commended for moving forward with the development of a low-yield and very accurate nuclear weapon, given the current lack of capability of conventional munitions to destroy deep bunkers. A future U.S. president should have the option to at least consider the use of such a weapon to prevent a nuclear-armed leader from attacking the U.S. homeland while limiting civilian casualties in a densely inhabited foreign city.

Third, the Mediterranean theater that Churchill faced in early World War II may represent a future model for warfare. Unlike the Atlantic, Churchill had to work in a very crowded space: the Germans in Italy, Greece, Crete and North Africa; the Italians in Italy and North Africa; and potential opponents in France and Spain. Enemy bases, planes and ships were never far off. In today’s world, the proliferation of precision-guided weapons has made the small distances of the Mediterranean and, especially, the Persian Gulf even more dangerous. These same weapons are shrinking distances even in the vast Pacific, insofar as Chinese forces can reach U.S. ships increasingly quickly. The Pacific of the future will resemble the Mediterranean of World War II more than the Pacific of World War II.