Dodging the Storms on the Longest Day

Perhaps the most difficult decision of World War II was made 75 years ago this week—and it was all about the weather.

The Germans had festooned the waters off the beaches with obstacles strewn with explosives to destroy landing craft, so the attacks had to take place at a time when the tide was low enough for these to be visible to the boat crews and demolition specialists. And there had to be moonlight for intense air operations. That helped determine 5, 6 or 7 June as potential dates for the assault.

Accurate weather forecasting was extremely difficult but vital. A great fear was that a storm striking after the initial force landed would leave the troops to fight, outnumbered and unsupported and unable to be retrieved.

For most of May, the weather had been ideal—calm with clear skies, flat seas and little wind—but that was about to change. Allied domination of the North Atlantic meant the Germans could not dispatch ships or aircraft to monitor the weather and they missed subtle changes that were noted by the British and Americans. So crucial was such information that in 1943 the Germans sent a U-boat to set up a weather station on the isolated coast of northern Labrador in what was the Dominion of Newfoundland, now part of Canada.

With the information available to them, the Germans concluded that the weather would remain too stormy for a cross-Channel invasion in early June. That sealed for the Allies the element of surprise. The German confidence was such that, in the days before the invasion, the officer in charge of coastal defences, Field Marshall Erwin Rommel, flew to Germany to ask Hitler for direct control over panzer forces and to deliver a birthday present to his wife.

The Allies, in contrast, received measurements of temperature, barometric pressure and humidity from ships, aircraft and weather stations stretching across Nova Scotia, Greenland, Iceland, the Faroes and Ireland, to the Azores and Canary Islands, and over to Bermuda and the Caribbean.

Anthony Cave Brown says in his book Bodyguard of lies that at lunchtime on 29 May, Stagg’s team received signals from aircraft monitoring the weather over Newfoundland indicating that a serious disturbance was building there.

By 1 June, more such disturbances were building out in the Atlantic with deep depressions identified between Newfoundland and Ireland. Stagg warned that weather prospects for 4, 5 and probably 6 June were not good. He told Eisenhower the situation was ‘potentially full of menace’. In his diary, Stagg described the agony of weighing this information with so much at stake as ‘a desperate quandary’.

By then Eisenhower was said to be a very worried man. He wrote later that when commanders assembled on the morning of 4 June, the weather report was discouraging: ‘Low clouds, high winds, and formidable wave action were predicted to make landing a most hazardous affair. The meteorologists said that air support would be impossible, naval gunfire would be inefficient, and even the handling of small boats would be rendered difficult.’

British general Bernard Montgomery was concerned about the great disadvantages of delay and argued that the operation should go ahead. Air Chief Marshal Arthur Tedder, Eisenhower’s British deputy commander, urged a postponement. A veterans of air operations going back to World War I, Tedder was particularly aware of the importance of providing the air support crucial to the operation and for getting the paratroops and glider troops to France and safely onto the ground.

Eisenhower decided to delay the attack for 24 hours. The weather in London then was calm and clear but conditions in the Channel quickly deteriorated, proving Stagg and his team right.

Some of the attacking contingents were already at sea and had to be recalled amid a constant fear that the Germans would note the activity and realise the invasion was imminent. The night was black and stormy, making the reversal of course difficult, and some of the smaller, flat-bottomed landing craft capsized, drowning some of those aboard. One minesweeping force was only 35 miles from the French coast but came home undetected.

Repeated radio signals to turn about did not reach a 138-ship convoy carrying US troops and there were no allied vessels close enough to intercept it. Little Walrus pusher-engined biplanes were sent through fierce squalls to find the convoy. One crew spotted it just before dark and flew low over the lead ship to drop a coded message from naval headquarters. The cannister missed the deck and sank into the ocean. The pilot wrote a note which landed on the ship and the convoy turned back.

On 2 June, Stagg observed that the whole North Atlantic appeared to be filled with depressions. He’d examined charts going back 50 years and could not recall one showing so many formations so intense at that time of year. But two days later, he noticed that behind an approaching cold front, a depression off Newfoundland was intensifying and deepening. While that revealed that a storm could be gathering, it also indicated that its progression towards the Channel was likely to be slowed.

Stagg concluded that between the advancing cold front and the depression could be an interlude of calmer weather long enough for the assault. If it eventuated, and if the supreme commander could be persuaded to take advantage of it, it might be a heaven-sent break. It occurred to him that the Germans might also detect this window. If they didn’t, they were likely to assume that the weather would remain bad.

Stagg explained all this to the commanders. Eisenhower pondered and, as wind and rain beat on the windows, he gave the order to remount the operation. As the landing craft moved in, waves were five to six feet in mid-Channel, higher than expected but survivable. If the invasion had been delayed, the next possible window, 19 June, would not have worked. On that day the Normandy beaches were struck by a massive storm. Any further delay could have seen the operation delayed until the following spring.

Eisenhower noted that a reinforced division used 600 to 700 tons of supplies daily. With 36 Allied divisions in action, that meant around 20,000 tons of fuel and other supplies would have to be trucked from the beachhead to the advancing troops each day.

To avoid the costly exercise of capturing a port, the Allies built giant floating cassions which were towed across the Channel and submerged to form two harbours called Mulberries, one on a British beach and one servicing the American forces. The storm destroyed the American Mulberry.

For four days, it stopped almost all landings of additional troops and supplies and ‘it was so fierce in character as to render offensive fighting extremely difficult’. An American division waiting to disembark had to ride out the storm, seasick and exhausted.

When the storm abated, Eisenhower flew along the beaches and counted 300 wrecked vessels ‘above small-boat size’ which had been hurtled onto the sands. ‘There was no sight in the war that so impressed me with the industrial might of America as the wreckage on the landing beaches. To any other nation the disaster would have been almost decisive; but so great was America’s productive capacity that the great storm occasioned little more than a ripple in the development of our build-up.’

Eisenhower later wrote to Stagg saying: ‘I thank the gods of war we went when we did.’

Brendan Nicholson is defence editor of The Strategist.

This article appeared originally at The Strategist (ASPI).