At 51 miles per hour, chasing down a runaway train was surprisingly the easy part. The hard part was catching it without sending the whole thing off the rails.

On May 15, 2001, a CSX locomotive known as “Crazy Eights” rolled out of an Ohio rail yard with no one controlling it, 47 cars behind it, and toxic chemicals onboard. For almost two hours, authorities tried to stop it as it barreled through small towns and headed toward a dangerous stretch of track. At one point, the situation became so desperate that police were told to “shoot the damn thing.”

Then, two railroad workers were asked to try something that sounded impossible: catch the runaway train from behind.

Engineer Jess Knowlton and conductor Terry Forson weren’t trying to ram the train. They had to close the gap, match its speed, line up the couplers, and connect it while the unmanned locomotive ahead was still pulling at full throttle.

In Pop Mech’s thrilling feature, “A 3,000-Ton Locomotive Was Loose, Unstoppable, and Filled with Toxic Cargo,” Jesse Hicks explains the danger behind the daring rescue attempt:

The plan was simple in theory but perilous in practice: They had to couple their locomotive to the runaway’s last car, matching speeds on the open main line. A single mistake—coming in too fast—could send both trains off the rails. In a yard, coupling normally happens at a crawl, maybe four miles an hour. Here, Knowlton had eased his engine down to 51 mph, trying to align perfectly with the speeding Crazy Eights.

The important thing to remember is how gently the two trains had to meet. Railroad couplers are built to lock together when they line up correctly, but the contact still has to be controlled. In one Federal Railroad Administration locomotive coupling test program, researchers found that equipment damage began at coupling speeds of 6 mph—so, in this case, the danger wasn’t simply in how fast the trains were moving down the track, but how hard they hit each other.

Fortunately, Forson had picked up one small detail that made the attempt possible. As Crazy Eights rolled past, he saw that the rear coupler (the “knuckle”) was open. That meant there was a chance he could connect his locomotive to the runaway from behind. He still had to line it up perfectly while both trains were moving at speed.

He eased his locomotive into position. To Knowlton’s relief, the couplers came together on the first shot. “I’ve had harder hits in the yard than what we hit that train with,” Knowlton said. CSX 6462 had joined Crazy Eights. But the ordeal was far from over.

But coupling onto the runaway didn’t stop it. The engine was still pulling at full throttle, with 47 cars between it and Knowlton’s locomotive. He couldn’t just slam on the brakes or try to drag the train backward. He had to slow it carefully and use his locomotive’s braking system to take speed out of the train, bit by bit, without causing the cars between them to buckle, separate, or come off the rails. It was a remarkable maneuver with almost no margin for error.

But how did the train get loose in the first place, why did the early attempts to corral it fail, and how did a two-hour disaster miraculously end without catastrophe? Read the full exhilarating story now for the answers.