It was a Tuesday, seventy-six years ago, on June 6, 1944, when Allied forces landed at Omaha Beach with the largest amphibious invasion in history.

Codenamed Operation Neptune, D-day began the liberation of France, and laid the foundation of the Allied victory on the Western Front of World War II.

D-day has been well documented in countless books and films throughout the intervening decades, but it was such an incredible operation that it’s almost impossible to know everything about it.

For example… what the “D” signifies. It simply signifies day, and was traditionally used for any significant military operation. So the day before the operation was D-1, similar to the way “T” signifies the time in a rocket launch countdown.

Here are five other amazing things you probably didn’t know, courtesy of History.com

1. A black combat medic saved perhaps hundreds of lives but never received the MOH
Waverly B. Woodson, Jr.was a member of the Army’s segregated 320th Barrage Balloon Battalion, the lone African-American combat unit to fight on D-Day. When his landing craft hit the beach, it was hit by a German which blasted it apart, killing the man next to him. Woodson was peppered with so much shrapnel he thought at first he was a goner too.

But CPL Woodson managed to set up a medical aid station and for the next 30 hours, removed bullets, dispensed blood plasma, cleaned wounds, reset broken bones and at one point amputated a foot. He also saved four men from drowning. Woodson saved dozens if not hundreds of lives.

But he was never awarded a Medal of Honor for his heroism. Woodson passed in 2005, but his family and members of Congress have petitioned the Army for years to review his case for a posthumous award.

2. Historians still to this day don’t know exactly how many soldiers died at D-Day
There is no doubt that thousands of troops gave the last full measure of devotion during the initial phases of the Normandy Campaign, but military records aren’t clear as to the exact dates.

The U.S. Military knew the casualties would be high during the invasion. General Dwight Eisenhower was informed by military strategists that just paratrooper casualties alone could be as high as 75 percent.

In the late 1990’s when a memorial was first being planned, fatality estimates ranged from 5,000 to 12,000. Historians estimate there were 4,414 Allied deaths on June 6, including 2,501 including 2,501 Americans. But the figure is just that: an estimate. We may never know.

3. Almost nothing went according to plan
The strategy on D-day was to first heavily bomb Nazi gun positions at the coast and destroy key bridges and roads, cutting off the enemy’s retreat and reinforcement. Then paratroopers would drop in to secure inland positions as the land invasion began on the beaches.

But bad weather and visibility meant the bombers failed to take out the key artillery. Many paratroopers were dropped far off their marks. And then, a critical fleet of marine tanks sunk in stormy seas and never even made it ashore. Yet, our boys persevered and prevailed.

4. But the Nazis got it wrong too.
As early as 1942, Hitler understood the war in Europe could be lost with a large-scale Allied invasion of France. His nightmare became a reality.
In large part due to a brilliant Allied deception campaign, Hitler believed the invasion would occur over 200 miles away at Calais where the Germans installed three massive gun batteries. But they left the Meanwhile, they left the rest of the French coastline—including the northern beaches of Normandy—much less fiercely defended.

5. Letting down the landing ramp was one of the most harrowing jobs during the invasion
Frank DeVita was only 19 years old when he had the responsibility of dropping the ramp of his landing craft at Omaha Beach. “This was our shield as long as it was up. And as we approached the shoreline where the water hits the sand, and the machine guns were hitting the front of the boat—it was like a typewriter,” DeVita remembered.

When he was ordered to drop the ramp, DeVita paused. “I figured in my mind when I drop that damn ramp, the bullets that are hitting the ramp are going to come into the boat. So I froze.”

But ultimately DeVita followed the order. “I dropped the ramp,” he said. “And the first 7, 8, 9, 10 guys went down like you were cutting down wheat…They were kids.”

6. Eisenhower almost quit his job months before the invasion.
The Allied forces weren’t always allied in their thinking. A few months before D-Day, Commander of the Allied Forces, Dwight D. Eisenhower and England’s Prime Minister Winston Churchill found themselves at odds over a critical part of the plan.

Eisenhower wanted to start bombing critical French infrastructure, shifting away from German industrial plants. But Churchill and some of his strategic advisors, including Arthur “Bomber” Harris of the Royal Air Force strategic bomber command didn’t agree. Churchill in particular worried about collateral damage to France and wanted to nix the idea.

So Eisenhower threatened to quit. In the end, he got his way (obvi) and France was liberated.