Speed record untouched for decades
For no more than a couple of minutes on July 3 1938, Mallard thundered along at speeds that have remained unmatched by any steam locomotive for three-quarters of a century.
A handful of men in soot-stained overalls had pushed the roaring engine to 126mph, and in doing so had marked the pinnacle of steam power.
Now, seventy-five years to the day, Mallard will be reunited with her five surviving sister locomotives - two of which have been shipped from North America and restored - to commemorate her record-breaking run.
The event at the National Railway Museum in York is such a huge undertaking it will be "a once-in-a-lifetime celebration", organisers said. "What we're planning is a major celebration - people will be coming from four corners of the earth," Anthony Coulls, the museum's senior curator of rail vehicle collections, said. "The gathering of the six locomotives is the jewel in the crown really."
Despite its unique place in history, Mallard was one of 35 near identical A4-class locomotives designed by renowned engineer Sir Nigel Gresley - the man behind the Flying Scotsman.
The six survivors include Dominion of Canada, which now sits next to Mallard at the National Railway Museum after it was shipped from Montreal last October and restored especially for the anniversary. And the Dwight D Eisenhower - another transatlantic expat - has also rolled back into York and been treated to a scrub-up for the occasion.
Union of South Africa and the Sir Nigel Gresley, will join them around the museum's Great Hall turntable for what organisers have dubbed The Great Gathering.
Bittern, the final survivor, travelled from London Kings Cross under its own steam on Saturday after it was granted special permission to make a celebratory 90mph run up the East Coast Main Line to York - 15mph over the normal limit for steam trains. It reached a top speed of 92mph and arrived on time.
Modelled in a wind tunnel, the Doncaster-built A4s' swooping art deco lines made them look like they were breaking records even when they were standing still. But LNER's prime objective was simply to build a fleet of luxury express trains for its high-speed East Coast Mainline service, and one of the most long-standing speed records in history happened virtually by chance.
Mallard is thought to have been plucked from the pack because it was one of the newest locomotives and was fitted with a new performance exhaust, which Gresley wanted to test on the engine's home turf - the East Coast Mainline near Grantham.