On June 6, 1944, Allied forces stormed the beaches of Normandy. In the August 1944 issue, Popular Mechanics published "How the Invasion Was Planned," detailing how the huge land assault came together. Here is that story.

In speaking of the greatest military assault in history—the invasion of France by the Allied forces—Prime Minister Churchill said:

"Everything proceeded according to plan. And what a plan!"

The magnitude of that plan, worked out by persons Herr Hitler once called "military idiots," staggers the imagination. It embraced the air, ground and sea forces of this nation and our allies. It hurdled problems of supply and transport, of pre-invasion training, of production and improvement of weapons, of photo-reconnaissance and mapping on a scale that makes the battle plans of Napoleon look like a game of checkers. More than 125,000,000 maps alone, just to mention one item, were used in perfecting the master invasion plan.

The success of that plan was demonstrated to a stunned enemy and a surprised world on D-Day. Four thousand ships carried the magnificently equipped troops across the English Channel under protection of a powerful naval force including 12 battleships, and thousands of aircraft.

Parachute and airborne divisions, spearheading the invasion, filled the sky over Normandy. As a climax to the "combined operations" attack on German coastal defenses, Allied planes dropped 11,000 tons of bombs in the eight hours preceding the landing and big naval guns pounded the coast before the troops went ashore. In 10 minutes, 600 naval guns fired 2,000 tons of shells at Nazi batteries.

Behind the invasion plan were lessons learned the hard way on the beaches of Dunkirk, Dieppe, North Africa, Sicily, Salerno, Anzio, Attu and Kwajalein.

After the general timing for the invasion was set at Teheran, the exact site for the landing was decided upon. This remained a closely guarded secret until H-Hour on D-Day. The low sandy beaches of Normandy between Le Havre and Cherbourg were selected not only for their proximity to great bases and supply depots in England, but because the region was suitable for amphibious operations and the defenses were within easy range of our aircraft.

"Everything proceeded according to plan. And what a plan!"

The Norman coast, however, was just about the center of Hitler's famous West Wall. German boasts about the invulnerability of this West Wall acted as a boomerang, for they inspired the most careful reconnaissance in military history.

What happened to this West Wall on D-Day? The answer forms a revealing chapter in the invasion plan. For months our troops had been storming a replica of that West Wall set up along the coast of England.

From information obtained from Commando and Ranger raids on the French coast, from the French underground, from photo-reconnaissance, from scouting parties in small boats and midget submarines came a complete picture of German coastal defenses. The only think missing was the secret rocket weapon which the Nazis threatened would blow England to bits.

The Nazi shore defenses consisted of a ring of tubular steel scaffolding build under water 150 yards out from the high water line, and behind this a double apron of wire fence, concrete antitank barriers in zigzag arrangement with protruding steel prongs (called "horned scullies" by our troops), and another double apron of wire fence. On the beach above the high water line was a three-foot barbed wire fence, a mine field, and intricate deep wire obstacle, an antitank ditch, concrete antitank wall, and "dragon's tee"—concrete blocks to stop tanks. Behind this maze of beach defenses were pillboxes; farther back, heavy artillery. With the mined waters off shore—which were cleared by minesweepers during the early hours of D-Day— this composed the coastal sector of Hitler's West Wall.

A duplicate of these defenses was built by American and Royal engineers at a pre-invasion training base. When the assault divisions of engineers and infantry arrived in the first landing barges, they knew how to blast a gap through these barriers. After the engineers had cleared a path for the assault infantry to advance on the pillboxes, the first heavy equipment to come ashore was the bulldozers.

One paratroop innovation in Normandy was the dropping of dummies, which confused the Germans

These bulldozers with armored cabs roll off the barges pulling sleds with steel mats to build roads across the soft sand. If a tank or piece of heavy artillery is hit by an enemy shell, or a truck bogs down, the bulldozers push them out of the way and the supplies move on. Some of the bulldozers were carried ashore from LST's and other landing craft on the Navy's new "Rhino Ferry," a self-propelled barge of light welded steel pontoons. These pontoons, one of scores of innovations developed for the invasion, can also be put together to form floating wharves and causeways.

Airborne divisions were used on a scale that dwarfed the German landings at Crete and our own in Sicily. An airborne division is made up of a regiment of paratroop infantry, two glider regiments and miscellaneous units, such as engineers, quartermaster, signal corps, medical and others. One paratroop innovation in Normandy was the dropping of dummies which confused the Germans as to where the real landings were to be made. Adding injury to insult, some of the dummies were filled with explosives.

The spearheading paratroopers, all with particular jobs to perform and special targets to attack, cleared strips for the "one-mission" gliders to land men and equipment. Some gliders carried light tanks. The glider regiments quickly build landing strips for the troop transports. The location of these airstrips was selected months in advance from aerial photos. The calculations from these photos are so accurate that the number of cubic yards of earth to be moved can be closely estimated. This careful planning was one reason five airstrips were completed a few days after D-Day. This was an important factor in the rapid advance and the joining up of airborne and seaborne infantry to consolidate positions along 60 miles of coast.

While troops were training and great piles of material were accumulating in England, our air fleets were carrying out a plan for strategic bombing of enemy targets. On their "priority" list were submarine pens, aircraft, munitions and armament plants, oil refineries, synthetic rubber factories and all industries producing goods for the Nazi machine. The Luftwaffe's wings were pinned back in the air and on the ground, according to plan. The result was that on D-Day Allied Supreme Headquarters could estimate the Germans had a maximum of 1,750 fighters and 500 bombers to combat the 7,500 Allied planes operating with the invasion forces. The plan worked so well that the weakened Luftwaffe left the sky to the Allie on D-Day.

The air attack wound up with a 50-day assault on enemy transportation extending several hundred miles inland from Holland to the Bay of Biscay. Ninth Air Force fighter bombers and rocket-firing R.A.F. Typhoon fighters threw enemy transportation and communications into chaos. American Mustangs, Lightnings and Thunderbolts added "strafe bombing" and "glide bombing" to the familiar technique of dive bombing. In strafe bombing, the fighters come in low and plant delayed-action bombs before pulling up to almost 90 degrees. In glide bombing, the angle of descent is more gradual than in dive bombing and the ascent much sharper. At 400 to 500 miles an hour, the planes are too fast to be tracked by Nazi flak batteries.

The region around Caen was marked on the master invasion plan as the focal point for pre-invasion bombing, but care had to be taken not to tip our hand in advance of D-Day. Twenty-one days before D-Day airfields and communication centers were bombed within 130 miles of Caen.

The plan worked so well that the weakened Luftwaffe left the sky to the Allie on D-Day

The next step was a concentrated assault on coastal batteries, set in 30 inches of concrete, along the invasion site. This attack was carried out on the eve of D-Day and repeated 30 minutes before H-Hour. Night and day fighters were used, in the final assault joined by 1,350 Flying Fortresses and Liberators. The 11,000 tons of bombs mentioned earlier, were dropped in this final phase.

During the actual landing, fighters covered every beach operation. American Thunderbolts flew high cover, British Spitfires flew low. Night bombers laid smoke screens. Other planes protected the convoy across 70 miles of channel.

One of the greatest problems for the invasion planners was the shipping of gigantic stores of fighting equipment and supplies to England, assembling the equipment and distributing it to coastal depots. Every one of the thousands of men landed in France required about 10 ship tons of overall equipment, and an additional ship ton every 30 days. The number of separate items needed was about a million. Some of these million items had to be accumulated in millions, resulting in astronomical totals. These supplies, ranging from M-4 tanks, 240-mm howitzers and flame throwers, to bazookas, razor blades, and carrier pigeon free, were moved by ships on a rigid timetable.

For two years these supplies flowed steadily to depots scattered over England. The Army Service units—ordnance, engineers, signal, medical, transportation, quartermaster and others—built up stock piles so large there was no chance of putting many under cover. Fields were blanketed with guns, rocket weapons, amphibious vehicles such as the famous "duck," trucks, half tracks, bulldozers, ambulances. The only protection from enemy eyes at these open-air depots was camouflage and the fact that daytime flying was too unhealthy for the enemy over England. One Yank protested that if we didn't stop piling up equipment, the island would surely tip.

In one month, about 1,500,000 ship tons of cargo were shipped from New York alone.

One of the most effective new weapons in the invasion was a 50-pound rocket projectile that can be fired from ground positions, from barges, or airplanes, and can be loaded with explosives or chemicals for laying smoke.

The supply line extended back across convoy lanes, through U.S. embarkation ports, to depots in this country with 245,000,000 square feet of storage space. The process of moving supplies to England was gauged by the general timetable, radioed requisitions from supply officers in England, and the availability of ships. In one month, about 1,500,000 ship tons of cargo were shipped from New York alone.

When the convoys left U.S. ports, supply officers notified British ports of the contents, not only of the ships but of certain holds in the ships. In this way, supply officers in England earmarked items for the various depots so the goods could keep moving. Some of the high-priority cargo was moved by air as D-Day approached. Our commanding officers insisted on "amphibious packing" of goods so that they would remain intact after a dunking.



Aviation gasoline and fuel for tanks and trucks by the millions of gallons were stored. About 60 percent of the deadweight tonnage moved to front lines is gasoline and oil. Fuel must be transported in oil drums until tankers can get close enough to shore to connect with portable pipelines. These lightweight pipelines, used with great success in Tunisia, will ease the problem of oil supply for our army in Europe. They are far more difficult for the enemy to see than a tank truck, and a 100-pound bomb must strike within four feet to wreck the pipe. Even then it can be quickly repaired; a thousand feet can be laid in two hours.

While the Army was piling up supplies, transporting and training a huge invasion force, the Navy was constructing amphibious bases along the British coast. Navy and Army units practiced the loading and unloading of combat teams and equipment from dozens of types of landing craft.

All the time preparations moved ahead on a grand scale, Allied Supreme Headquarters maintained the strictest secrecy as to when and where the invasion army would strike. There were map rooms where even generals had to show special passes.

Although the Germans could not guess the place, they probably figured they could accurately set the time of day in accordance with the tides. Here they were fooled, for our invasion planners set the time four hours before high tide. Thus, most of the enemy shore batteries that had not been knocked out by our aircraft were caught napping. This plan was carried out even though General Eisenhower had to postpone the hour of attack 24 hours awaiting favorable weather.

As D-Day neared, the troops were briefed for their exact mission and reshuffled from battalions and companies into "craft loads," ready to move at a moment's notice. After briefing, the invasion camps were "sealed" and the mean were forbidden communication with unbriefed troops or civilians. These final security measures prevented any leaks as to the hour and place of attack after briefing thousands of men.

There were map rooms where even generals had to show special passes

When H-Hour came and the Navy and air crews moved the Allied forces across the channel, it was the culmination of the most minutely planned combined operation on record. The invasion forces were composed of inter-dependent units, a weak link in any one of which would have meant disaster. In the master plan, the air forces, ground troops, airborne divisions, and naval units were welded together to form the most powerful force ever hurled against an enemy shore.

They planned it that way.