The world's largest steam locomotive is heading to Philadelphia for the Fourth of July

For the first time, the world's largest steam locomotive is rolling into the Northeast — and it's arriving in Philadelphia just in time for the Fourth of July. Union Pacific's Big Boy locomotive has been turning heads across the country, drawing crowds from small towns and farms to big cities. When it rolls by, the train's full-throated whistle brings America to a standstill. "I've been wanting to see the Big Boy my whole life," said one onlooker. "I've never seen a steam train up close." A beast of an engine, built for war Originally built in 1941, Big Boy is the largest, heaviest, and most powerful steam locomotive in the world. Union Pacific built 25 of them during World War II to haul heavy cargo over the Rocky Mountains. Today, eight survive — but seven years ago, not one of them was running. Engineer Ed Dickens and his team took on the challenge of stripping down and rebuilding locomotive No. 4014 from scratch. "It was a dream come true," Dickens said. Asked whether the team had to hunt for replacement parts, he said: "We make the parts — we have all the blueprints." Rolling coast to coast for America 250 The cross-country journey is part of America's 250th birthday celebration. Along the way, Big Boy makes extended stops to give train enthusiasts and the curious a closer look at the historic machine. "It's just amazing — it touches my heart and my soul," said one spectator. Union Pacific CEO Jim Vena said the trip was designed to capture the spirit of the milestone. "It's America 250. It really is," Vena said. "We felt it'd be real special to say, celebrate going from the West Coast to the East Coast." The locomotive is now reminding the country of its industrial past — as it boldly powers into the future.