THE photograph shows a mysterious object wrapped in tarpaulins being transported on the back of an articulated lorry past Walmgate Bar in York.

But what on Earth was it? That's certainly the question the people watching it as it passed must have been asking themselves.

The date was sometime between January and April 1958. And the object - which at first glance, with its high tail, resembled nothing more than a whale - was actually the prototype of Britain's latest strike aircraft, the Blackburn Buccaneer.

Built at the Blackburn factory in Brough, East Yorkshire, the new aircraft had been designed as a Cold War-era carrier-based strike and reconnaissance aircraft. It was built to carry both conventional and nuclear weapons and to be able to approach Soviet warships below radar level. Its odd shape was the result of the wings being designed in such a way that the aircraft would be stable when flown at low level and would have a slow stall speed.

Before it could be brought into use, however, the aircraft - a precursor of the Sea Harrier - had to be test-flown. For that purpose, it was loaded onto the back of a transporter at the Blackburn factory in Brough, shrouded in a tarpaulin - then driven by road to the Royal Aeronautical Establishment test centre at Thurleigh airfield in Bedford.

That involved a detour through York in order to get to the A64 - hence that extraordinary photograph, and the other two we have today, showing the aircraft being transported at different points along its journey.

The Buccaneer's maiden test flight took place at 12.57pm on April 30, 1958 - in other words, exactly 60 years ago today. "According to test pilot Derek Whitehead, the flight went exactly as planned, with the aircraft...weaving gently as the pilot tested the controls whilst holding the aircraft at very low level," says Ian Richardson of the Yorkshire Air Museum at Elvington.

The Buccaneer - later built by Hawker Siddeley, which merged with Blackburn - remained in service with the Fleet Air Arm until 1978 (when it was replaced by the Sea Harrier) and with the RAF until 1994 (when it was replaced by the Tornado).

Some of the later development work on the Buccaneers was conducted at Holme-on-Spalding-Moor and at Elvington.

So it is little surprise that, during its 'Thunder Day' yesterday - when several aircraft were started up and their engines allowed to roar - the Yorkshire Air Museum chose to celebrate the 60th anniversary of the Buccaneer's test flight by firing up the engines of one of its Buccaneers: a Buccaneer S.2 which took part in the first Gulf War.

"It was flown into retirement here at Elvington on August 19, 1991, wearing RAF camouflage markings, and has been kept in live, ground operational condition since then," says Mr Richardson. "It has now been restored to its original Fleet Air Arm colours, and makes a very striking-looking aircraft.

So it does.