Around 10:30 pm. on the cold, moonless night of March 24, 1944, Johnny Bull slowly peeked his head out of the ground and filled his lungs with freedom as he breathed in the frigid air. The sweat-soaked prisoner of war had just poked away at the last nine inches of grass and dirt atop a vertical shaft at the end of a tunnel that ran more than 30 feet below the oblivious Nazi guards patrolling the Stalag Luft III camp, which held thousands of Allied airmen captured by German forces in World War II.

The flyboys who bravely soared the skies had demonstrated courage and ingenuity below ground as well in toiling for nearly a year to construct a tunnel that would allow them to flee from captivity. The secret plan had been led and organized by Roger Bushell, a Royal Air Force pilot who had been shot down over France while assisting with the evacuation of Dunkirk. After Bushell, nicknamed “Big X,” escaped twice from German prisoner of war camps, he was sent to what the Nazis believed to be one of their most secure facilities—Stalag Luft III. At this camp, 100 miles southeast of Berlin, the Nazis had taken measures to prevent tunneling, such as raising prisoners’ huts off the ground and burying microphones nine feet underground along the camp’s perimeter’s fence. In addition, the camp was built atop sandy ground through which it would be extremely difficult to tunnel. Still, Bushell would not be deterred.

In the spring of 1943, he and others began work on an audacious plan to construct three tunnels with the code names of Tom, Dick and Harry that would stretch over 300 feet to outside the camp’s perimeter fence. Under the rules of engagement of the Geneva Conventions, the penalty for being caught, generally 10 days in solitary confinement, was worth the risk.

Inside Hut 104, the prisoners of war building the Harry tunnel—who included many British airmen as well as Americans, Canadians, Australians, French and other Allied pilots—toiled for days chipping away at the building support columns to avoid being seen working underneath the huts. From a trap door concealed below a heating stove always kept lit to discourage the Nazi guards from getting too close, they burrowed down 30 feet in order to be out of the range of the microphones. Working in claustrophobic conditions, the prisoners excavated 100 tons of sand, which they stuffed bit by bit into concealed socks and discreetly sprinkled into the garden soil being raked by other prisoners. The diggers stripped to their long johns or took off all their clothes so that the bright golden sand wouldn’t stain them and raise the suspicions of the German guards.

The prisoners scavenged and stole materials for the operation. They stripped 4,000 wooden bed boards to build ladders and shore up the sandy walls to prevent collapse. They stuffed 1,700 blankets against the walls to muffle sounds. They converted 1,400 powdered milk tin cans provided by the Red Cross into digging tools and lamps in which wicks fashioned from pajama cords were burned in mutton fat skimmed off the greasy soup they were served. Eventually, some prisoners stole a wire that they then hooked up to the camp’s electrical supply to power a string of light bulbs in the tunnel. They fashioned a crude air pump system built in part with hockey sticks and constructed an underground trolley system pulled by ropes to transport the sand with switchover stations named after two London landmarks—Piccadilly Circus and Leicester Square.

By March 24, 1944, Harry was complete and all that was left was for Bull to break through the last piece of earth. One by one, the prisoners, dressed in civilian clothes and carrying forged documents, lay down on the rope-operated wooden trolley and were pulled through the 2 foot square tunnel to their escape. The process was tedious. Fewer than a dozen men made it through every hour, and a 1-hour blackout during a midnight air raid also slowed the operation.

Around 5 a.m.., a German soldier on patrol nearly fell into the exit shaft and discovered the tunnel. The prisoners inside scrambled back to the hut and burned their forged documents, while the Nazis mobilized a massive manhunt. They erected roadblocks, increased border patrols and searched hotels and farms. Within two weeks, the Nazis had recaptured 73 of the escapees. Only three men successfully fled to safety—two Norwegians who stowed away on a freighter to Sweden and a Dutchman who by rail and foot ended up in Gibraltar.

A furious Adolf Hitler personally ordered the execution of 50 of the escapees as a warning to other prisoners. In violation of the Geneva Conventions, the Gestapo drove the airmen, including Bushell and Bull, to remote locations and murdered them. “Escaping from prison camps has ceased to be a sport,” read posters the Nazis put up in the POW camps to warn future escapees that they would be shot on sight. In 1947, a military tribunal found 18 Nazi soldiers guilty of war crimes for shooting the recaptured prisoners of war, and 13 of them were executed.

Hollywood immortalized the breakout in the 1963 blockbuster “The Great Escape,” which starred Steve McQueen, James Garner, Richard Attenborough, Charles Bronson and James Coburn. However, the real-life heroes are the ones being honored this week on the event’s 70th anniversary. Yesterday, hundreds gathered in Zagan, Poland, to remember the victims and place wreaths at the exit point of the tunnel. Today, 50 serving Royal Air Force officers began a four-day, 105-mile march from the site of Stalag Luftig III to the British war cemetery in western Poland where the executed airmen are buried.