In the earliest light of August 19, 1942, 6,080 Allied troops, most of them Canadian, attacked the Channel port of Dieppe, France. They had orders to hold the port for two tides—about 12 hours—before withdrawing. The assault began with landings east and west of the town by commando units with orders to destroy a German radar installation and knock out coast artillery positions. Thirty minutes later, the main force, supported by Churchill tanks, struck Dieppe head on. Most of the tanks foundered on the town’s pebble and stone beaches. Most of the infantry were pinned down by German gun emplacements, undetected by Allied intelligence, which trapped them in a remorseless crossfire. Within a few hours, overwhelmed by horrific losses and the near collapse of inter-unit communications, the commanders on shore gave the order to withdraw.
The cost of the raid was appalling. Nearly a thousand Canadians were killed; hundreds more were wounded. Another 2,400 became prisoners of war. All in all, casualties reached 60 percent. And yet within weeks of this debacle, the Allied high command portrayed the Dieppe raid as a success: expensive, to be sure, but priceless in terms of lessons learned. In a speech before Parliament, Prime Minister Winston Churchill called it “an indispensable preliminary to full-scale operations.”
This appraisal was voiced even more emphatically by Lord Louis Mountbatten, whose Combined Operations Command had planned and executed the raid. Mountbatten even persuaded the journalists who had witnessed the raid to present Dieppe in the most favorable possible light. In 1943 American correspondent Quentin Reynolds published his eyewitness account as Dress Rehearsal: The Story of Dieppe. In it, Reynolds averred, “It would be safe to say that many American lives were saved in North Africa because of lessons learned in the dress rehearsal by the commando raid at Dieppe.”
After the war, Lord Mountbatten pushed the “dress rehearsal” theme to its logical conclusion. “The battle of D-Day was won on the beaches of Dieppe,” he insisted. The lessons learned at Dieppe had saved thousands of lives in the Normandy invasion. Dieppe, in short, “was one of the most vital operations of the Second World War. It gave to the Allies the priceless secret of victory.”
Implicit in Mountbatten’s assessment was the claim that the lessons of Dieppe could have been learned in no other way. Today military historians universally reject that claim. For one thing, many of the lessons were either common sense or else would have become apparent through study of other amphibious landings. For another, contrary to what Mount-batten insinuated, plans for the raid said nothing about testing the tactics for a cross-Channel attack. Nonetheless, it did indeed add to the operational lessons that factored into the planning for the D-Day invasion.
Among these were the importance of heavy naval and air bombardment prior to an invasion, the advisability of using airborne troops to isolate the beachhead, the need for better intelligence concerning German defenses and beach conditions, and a more robust communication system to counter the inevitable confusion of an assault’s early hours. It provided the inspiration for the “Funnies”—specialized tanks employed on D-Day to breach beach obstacles and swiftly move inland. It showed that unified command was essential: at Dieppe responsibility had been divided between ground, naval, and air commanders, each with competing priorities. And it exploded all hope of seizing a French port at the invasion’s outset.
Even cursory study of the planning for D-Day shows that these lessons were taken to heart—and yet a glance at the invasion of Tarawa in the Central Pacific and of Sicily and Italy in the Mediterranean indicates that those operations offered many of the same lessons. Thus, contrary to the impression Mountbatten sought to create, it did not require 60 percent losses in a doomed raid to properly educate the planners of D-Day.
But what if Dieppe had somehow succeeded? What if the assault teams had gone ashore, accomplished most of their objectives, and withdrawn on schedule and in good order? Admittedly, it is difficult to imagine a rewrite of history that could have produced this result. On the contrary, modern studies of the raid often devote half their length to the ways in which failure was seemingly inevitable. Yet war is always the realm of chance and probability. If the raid had been better planned, if the raiders had enjoyed better luck, and if the German defenders had been slower to react, it is just barely possible that the Dieppe raid might have ended in a small but glittering Allied victory.
Had that been the case, the lessons of Dieppe would have seemed quite different. Although D-Day planners certainly did not neglect the experience of other theaters, they tended to regard a cross-Channel attack as presenting unique challenges. Thus the example of a successful Dieppe raid would have exerted disproportionate influence. This is particularly likely concerning three key matters. First was the question of balancing the virtues of a heavy pre-invasion bombardment against those of tactical surprise. A successful Dieppe raid might well have tipped the balance in favor of the latter. Second was the need for tanks specially designed to support the early hours of a cross-Channel attack. Historically, the Americans rejected such tanks; but for the bitter experience of Dieppe, the British might have as well.
Third and most importantly was the question of seizing a port. Even before Dieppe, Allied planners had their doubts about whether this could be done. For that reason, prefabricated harbors—intended to be towed across the Channel and assembled off the invasion beaches—were already on the drawing board. Codenamed “Mulberry,” they could serve as a place to offload cargo in the absence of a natural harbor—as they would to great effectiveness in the D-Day invasion. But many naval officers looked askance at the Mulberries—one commander called them “the biggest waste of manpower and equipment that I have ever seen”—and the seizure of Dieppe would have offered tempting evidence that a port could be captured and that the Mulberries were therefore unnecessary. Needless to say, such lessons might have been fatal to the Normandy attack. But perhaps even worse for the Allies were the lessons the Germans might have learned from a successful raid on Dieppe.
Historically, Dieppe convinced many in the German high command that a cross-Channel attack could be stopped right at the water’s edge. “At Dieppe,” Hitler declared, “it needed only a regiment, engaged at the right time, to repel a raid which in a few hours might have involved three divisions. In no case must we allow the landing to last more than a few days—if not a few hours. The example of Dieppe must serve as a model.”
The raid therefore trumped the arguments of German commanders who favored a flexible defense based on a strong counterstroke by armored forces. By mid-1944, to be sure, Allied command of the air would have made such a riposte more difficult. But had the Germans studied the situation more closely and concentrated their tanks close to the handful of beaches the Allies might plausibly strike, a successful counterattack was hardly out of the question.
Conversely, a successful Dieppe raid would have been a strong argument against staking everything on a beachhead defense. Even if, as occurred historically, Hitler had continued to think of Normandy as a diversion, a major counterattack against the D-Day beaches would have been all but certain, because the release of armored reserves would have been standard doctrine rather than something requiring Hitler’s explicit approval. Thus, Lord Mountbatten may have been right after all—though not in the way he intended.