Mallard in its home in the National Railway Museum. Creative Commons 2.5 license

When it comes to Britain’s railway heritage, many people may regard the Flying Scotsman or even Stephenson’s Rocket as the most important railway steam engines, but for many rail connoisseurs there's another engine that remains synonymous with the heyday of British steam locomotives.

With its revolutionary aerodynamic design and shimmering blue paintwork, Mallard, designed by Sir Herbert Nigel Gresley, is one of the most beautiful, best-known and certainly best-loved locomotives in Britain.

It is also the fastest; on July 3 1938 the mighty A4 class loco reached an incredible 126 mph on the East Coast Main Line, breaking an existing German record of 124 mph set in 1936. It’s a world record for steam locomotives that still stands today.

This week sees the 70th anniversary of Mallard’s world-record-breaking run and the National Railway Museum (NRM) in York, which is now home to Mallard, is celebrating with a special reunion exhibition.

On July 5 and 6 2008 the NRM will be reuniting Mallard with three more of its streamlined contemporaries from the A4 class of locomotive. Billed as a ‘Great Reunion’ the weekend of celebrations will see Mallard, Bittern, Sir Nigel Gresley and Union of South Africa brought back together for the first time since their heyday.

There are only six A4 locomotives remaining in the world (the other two are in the US and Canada) and ticket holders will be paying £32.50 per person to see and take unique photographs of the four A4s.

Courtesy National Railway Museum

It’s a special date in the railway enthusiast’s calendar and the museum has already kicked off a week of events beginning with a re-enactment on July 1 of the record-breaking scene on the footplate of the world-famous locomotive with actor Chris Ford playing driver Joseph Duddington.

He was joined by Mallard experts and ex-drivers from across the North including David Court from Doncaster who has first-hand experience of driving an A4 locomotive at speed and a real idea of what drove Joseph Duddington to push Mallard to the limit.

“You've got a swirling mist of oil and coal dust in the cab,” said David. “If you touch your face it’s greasy, and of course the coal dust is swirling so it sticks to your skin and you look like a chimney sweep by the time you get off.”

“The thing was they knew what they were doing. They were going for it and so they'd all be keyed up. Tommy Bray would be seeing to his fire, Joe Duddington would be watching to see that everything was OK as regards steam, that the water was OK…”

“They went for it and they did it - 126 mph," added David. "It's unlikely that they would have got any more because when they touched 126 for them few seconds the engine and the bearings wouldn’t have stood much more.”

The fact that Mallard and her crew went for it so effectively is testament to the skills of Sir Nigel Gresley, one of the most gifted engineers Britain has ever produced. Gresley designed the A4 class of streamlined locomotives for running at sustained speeds of more than 100 mph, while the three-cylinder design made for stability at high velocity, and the large driving wheels offered maximum speed.

Courtesy National Railway Museum

Of all of Gresley’s A4s, Mallard was the fastest and, at the time of the record attempt, it was also the newest. Equipped with its double chimney and blast pipe it was nicely broken in, which made for an altogether more efficient machine – a fact that booked it a spot in the history books.

“It is testament to Sir Herbert Nigel Gresely’s brilliance that 70 years on Mallard’s record is still unbroken,” said Chris Nettleton, Secretary of the Gresley Society. “Gresley is one of the greatest engineers the world has ever known and it is only fitting that the NRM are taking this opportunity to demonstrate the sheer genius of his work with the upcoming Great Reunion.”

Gresley’s A4s may have been the first streamlined locomotives ever built in Britain but for many admirers visiting the NRM over the coming weekend, they were the most beautiful too.