A desolate anniversary. But perhaps one from which we can take some spirit.

21 May. If you’re British, French or Belgian, it’s a good moment to surprise, consternation, disarray and loss.

Not many years before this day 75 years ago, two of the victors of World War One, Britain and France, had been dictating terms to their humiliated foe, Germany. Now, in 1940, French and British armies with some remnants of Belgian units, were facing an abyss of utter disaster.

The Western Front in the Second World War hadn’t followed the pattern of the First. After eight months of sporadic but limited fighting, Germany had launched an offensive into France. One of the best tank commanders ever, Heinz Guderian, made sure they didn’t get trapped into trench warfare again by leading a long, powerful, and rapid attack to cut off a large group of his enemy. French and British reeled in front of him, in disorganised retreat towards the coast.

It took just eleven days to leave some 400,000 Allied soldiers with their backs to the English Channel, pinned down by 800,000 Germans. The British Commander, Lord Gort, decided that there was no way of breaking out, and started planning an evacuation – without telling his French allies.

Of the Channel ports that could have been used, Boulogne fell to the Germans and Calais was surrounded. In any case, the best to use was Dunkirk, with a good harbour and the longest beach in Europe. Churchill ordered full-scale evacuation to begin on 26 May.

British troops being evacuated from Dunkirk

Two key players now step onto the stage. One was Guderian’s immediate superior, Gerd von Runstedt, who, afraid of a counter-attack and the marshy nature of the terrain, issued the so-called “halt order”, confirmed by Hitler. This overruled Guderian and obliged him to stand still for three days when he might have wiped out the British and French forces as fighting units.

To this day, no one understands the reasons for the order, but it was a turning point: had the British Expeditionary Force, the army that had been sent to France, been destroyed, Britain might have been unable to fight on.

The second key figure is less well-known than he deserves. Admiral Bertram Ramsay had retired from the Royal Navy in 1938, possibly over the lack of preparations for the coming war. However, when fighting broke out, Churchill talked him back. He took command of Dover-based operations, so he was in charge of the Dunkirk evacuation.

Bertram Ramsay: logistical genius

The experience turned him into an expert in the logistics of major amphibious operations. He handled the landings in North Africa, Operation Torch, the landings in Sicily, Operation Husky, and finally, his crowning achievement, the landings in Normandy on D-Day in 1944, where he had overall command of the Allied naval forces.

This was a time before computers, and all orders had to be typed by hand. There were 5000 sets of orders for D-Day, and it’s a tribute to Ramsay’s organisational ability that the operation went so smoothly (the only hitches were those inflicted by the Germans): ships picked up the right troops, equipment or supplies, and delivered them to the right place as expected.

Back at Dunkirk, he organised the long convoys of ships, naval and civilian, big or small, that travelled across the Channel to pick up the soldiers, from the harbour or the beaches. The little ships have become legendary: they were often privately owned boats that travelled across and ferried soldiers out to the larger naval vessels to travel back across the Channel. 311 out of 693 British boats were little ships, and 170 out of the 226 lost in total.

Little ships at Dunkirk

In the end, 338,000 soldiers were brought to England. Not all the French were left behind: 100,000 were evacuated. They, however, were for the most past then shipped back to France to continue the defence of their country, generally only meaning that they were killed or captured a little later than they would otherwise have been.

The British forces evacuated formed the core of a renewed army that could continue the war, to its final victory. Their return therefore left the country breathing a sigh of relief, though Churchill made it clear there was no cause for celebration: “we must be very careful not to assign to this deliverance the attributes of a victory. Wars are not won by evacuations.”

And let’s not forget another group of Frenchmen: 35,000 stayed on fighting, as a rearguard, allowing the evacuation to continue until 4 June. Many were killed, the rest captured. Their sacrifice made the rescue of British forces possible. As did the brilliance of Admiral Ramsay. And the ineptitude of Runstedt and Hitler. Of such strange mixtures of heroism, ingenuity and incompetence are narrow escapes made.

The experience also gave us what we have come to know in Britain as the Dunkirk spirit, a refusal to accept defeat, a willingness to pull something out of the fire whatever the odds, in order to fight again another day.

It’s particularly important for us in the Labour Party as we contemplate the wreck of our hopes in the face of the debacle the Conservatives handed us two weeks ago. Oh, well. Those lads at Dunkirk on 21 May 1940 faced a prospect even bleaker than ours. And in the end their side that came out on top…