New York Subway Extension Opens

May 21, 1904 saw the opening of a key extension of New York City's original subway, connecting additional Manhattan neighborhoods with the IRT's innovative electric multiple-unit trains. Engineer William Barclay Parsons led design efforts that conquered challenging bedrock and groundwater conditions. This expansion followed the system's inaugural run just weeks earlier and quickly carried thousands of daily commuters. It featured classic cast-iron stations and accelerated the city's northward growth. The project reflected broader Progressive Era infrastructure booms and set standards for rapid transit worldwide, influencing subway designs from London to Tokyo.