Chris Penney is a freelance writer covering aviation and military history, and is a member of Taunton Deane Conservatives.

In one of her last acts as the Conservative Party’s leader, Theresa May will attend the D-Day 75th anniversary commemorations at Southsea in Hampshire on Wednesday.  Surrounded by fellow leaders, she will doubtless derive some comfort from the fact that they represent NATO partners rather than EU antagonists.  But as she looks out over the Solent and the English Channel beyond, I wonder what she’ll be thinking?  If only Brexit had proved as successful as D-Day, perhaps?

To the casual observer, D-Day is the story of a mighty multinational force unleashed from southern England successfully landing in Normandy with the result that, less than a year later, the war in Europe had been won.  Yet at almost every stage of the preparations for this assault on occupied Europe, there was disagreement and division.

From before its start, those nations taking part had very differing outlooks on the conduct of the war, and these had to be ironed out before detailed planning could commence.  Other factors at play were command rivalries, clashes of personally and egos, arguments on every level about strategy and goals, conflicting advise from experts and even a breakdown in collective responsibility that needed addressing.  Such was the task facing the wartime allied commanders working up their D-Day plans.

In trying to decide when, where and how to assault Nazi Europe the allies had some experience to call on.  As early as 1940, Britain and France had attempted a landing in Norway.  The debacle lead to the famous Norway Debate in the Commons that sealed Neville Chamberlain’s fate.  The fatally-flawed Dieppe raid in 1942 lead to grievous Canadian losses, and proved that a defended port couldn’t be taken from the sea.  The Sicily landings highlighted problems of friendly fire, and the later Anzio landings exposed the tragic decision not to push inland at the earliest opportunity.  It’s often overlooked that by the time of D-Day on June 6 1944, the Allies were already ashore and fighting their way up the spine of Italy in what many veterans often cite as the forgotten European campaign.

Once it had been decided that the US would take the lead on D-Day, with the appointment of General Eisenhower as overall commander, he had to bang service heads together to achieve his aims of delivering the assault at a time and place of choosing.  Some factors were outside his control.  The weather would dictate suitable conditions for a landing, and the operation was tied to a period of moonlight for the nightime parachute and glider landings and lowest tide level for the dawn beach landings.  This severely restricted the number of nights each month when conditions were right to launch D-Day.

The Dieppe raid had also highlighted that control of the air over the Normandy area was a prerequisite for the landings to take place.  Trying to persuade the strategic bomber arms of both the RAF and US Army Air Force to redirect their heavy air power in support of the operation proved nigh on impossible, and Eisenhower had to threaten to resign to force the issue and get his way.  The bomber barons didn’t like it, but they had no choice: the cause was momentous.  There were then arguments about the bomber target list – oil versus transport.  Air commanders had to be summoned to a council of war meeting in March to be told taking out rail and road links in the assault area would be the most effective way of reducing German fighting capacity in Normandy, even though intelligence staff thought otherwise.

There were also some big personalities involved in the chain of command, all keen to stamp their authority on proceedings.  Churchill, remembering Gallipoli, ensured he had his say on matters that would rebound on him were they not successful.  Montgomery was his own man, and US army commanders viewed him with suspicion, saying that he lacked confidence.  Leigh-Mallory, who was in charge of the ground support air operations, had to be carefully sidestepped, to avoid empire-building ambitions getting in the way of the real military objectives, and always in the background there was the enigma that was de Gaulle.

To ensure D-Day was successful, ingenious ‘out of the box’ ideas were required.  It was recognised that reinforcements had to be landed during the follow-up phases fastr than the Germans could concentrate their reserves to repel the landing force.  This led to the design of the Mulberry floating harbours constructed in England, and towed across the Channel to form an instant port for the unloading of fresh troops and supplies and the evacuation of causalities.  If there was one invention that contributed to D-Day’s overall success then surely this was it.

Behind the scenes, there were the unsung heroes.  The naval planners that had the unenviable task of ensuring that over 5,000 ships were convoyed to deliver a simultaneous landing.  The army logisticians who had to make sure that every soldier and tank was where it was supposed to be when the army demanded it.  The air intelligence analysts who provided the targeting information upon which the supporting air attacks were based.  And in an era without computers, the typists who had to create the orders of the day upon which everything happened.  Years and years of planning and staff work came together to ensure nothing had been left to chance, and Eisenhower didn’t need the speech he had prepared announcing to the world that D-Day had failed.  As a result, Churchill never had to face a Norway-style grilling by parliament.

D-Day was never a guaranteed success, and there is much to admire about the single-mindedness of military purpose that overcame so many obstacles to accomplish it.  A year later, the only fighting still taking place was in the Far East.  It’s a lesson from history that is still relevant today.