It was a miserable September day in 1934 at the John Brown shipyard but it did not stop 250,000 people, clad in overcoats and huddling under black umbrellas, turning out to see the much-anticipated launch of ship number 534, soon to be officially named RMS Queen Mary.

When the bottle cracked open on the gigantic steel hull that had towered over Clydebank like a skyscraper, the biggest and most powerful ship in the world slid smoothly into the Clyde. There were sighs of relief all round. The biggest miracle was not that this mighty queen of the North Atlantic managed to squeeze into the tight fit of the river, it was that she was built at all.

The Queen's words - "I am very happy to name this ship the Queen Mary" - were carried across the world by wireless for the first time and heard as far away as Australia. Closer to home they were rejoiced by Sir Thomas Bell, of John Brown, and Sir Percy Bates, of Cunard White Star Line, who a few years previously thought this day would never come. The jubilation was shared with shipyard workers who raised their bunnets in the air and shouted "hooray" as the Queen Mary eased down the slipway at the beginning of a journey that would see her spend more than 25 years as a luxury liner popular with the rich and famous either side of a six-year stint as a Second World War troopship.

"It's a complex and interesting story and one that was right up there in the national headlines as it was such an epic contract for such a magnificent ship," says Ian Johnston, historian and author of several books on the Clyde's shipbuilding heritage. "The Depression of the 1920s had brought a number of companies that had grown because of the First World War to their knees. John Brown was primarily an armaments company and in the 1920s with austerity and depression it was in hard times. A number of big British companies bit the dust.

"In Clydebank, John Brown specialised in all sorts of ships, including these prestigious liners, and they had a very close relationship with Cunard. The last Cunarder they built was the Aquitania, completed in 1914 just before the First World War. So Cunard naturally looked to John Brown when it wanted to build two very large ships [which would become the Queen Mary and Queen Elizabeth] for the North Atlantic service."

By 1926 there were more firm ideas about what the first of those ships would be - it had to be big and it had to be fast. "Cunard developed their ideas in tandem with personnel at Clydebank, where there was a huge tank that was about 450ft long to test models. And in the drawing offices they had a room that was kept semi secret. A small number of young naval architects were put in there and told not to say a word to anyone in the shipyards, it was all secret," says Mr Johnston.

The men, some of the finest in the industry at the time, had started work on what was to become the Queen Mary, but first the job had to go out to tender. All the leading yards in the country pitched for the work but it was a foregone conclusion it would stay on the Clyde.

"Cunard thought so highly of John Brown: they were exceptional, they were so trustworthy, they built on time, they built to cost and the quality of the work was superb. Cunard trusted them implicitly and so did the British admiralty, which is why so many important warships were built there too over the years," says Johnston.

With the order placed at John Brown in December 1930, work started immediately. It was a blessing to the thousands of families who depended on the yard for an income because all previous orders at the shipyard had been completed; the Queen Mary was the only job in town. In its heyday, during the years of the First World War, John Brown employed about 11,000. When it came to the time of the Queen Mary things were so bad that total was down to about 3000.

Cunard had thrown the town a lifeline but it did not stay afloat for long. Within a year, as the ship quickly started to take shape, the chairman of Cunard telephoned Sir Thomas Bell at Clydebank to tell him work would have to stop because they could not raise the money to make the payments. The Wall Street Crash and the situation with the international money markets meant interest rates had gone through the roof. Work on ship number 534 was immediately suspended.

"At Clydebank work stopped and they had to post notices on the gates of the shipyard to say that, as of this morning, work on the ship would be stopped, and everybody was laid off. The men were all paid what they were owed and that was basically the end of it. There were just a few people left in the shipyard, down from more than 10,000 to just a few hundred, and 12 or 13 men were allocated to the ship, just to watch it and make sure nothing was starting to sink and to ensure it was in good condition," says Mr Johnston.

"They were hopeful it would be restarted early in the new year. John Brown and all the local MPs petitioned the Government to say, 'You can't leave this ship, this is a national icon.' The Queen Mary had become emblematic of the condition the United Kingdom was in - there was unemployment everywhere. These were terrible times and this ship represented the tragedy that had happened across the country."

Prime Minister Ramsay MacDonald refused to put any money into the ship and it lay at Clydebank for two years before a deal was finally brokered between the Government and the newly named Cunard White Star Line as work resumed in April 1934. "On the day work restarted a local pipe band piped the men through the main gate at John Brown's and she was brought very quickly to the launching stage, which is

the anniversary that is being celebrated this month," says Mr Johnston.

To put in context the salvation that work on the Queen Mary offered Clydebank, take a look at the bigger picture: shipbuilding was collapsing from the late 1920s onwards, not just on the Clyde but all over Britain. Adjacent to John Brown in Dalmuir was Beardmore, a huge shipyard and bigger than John Brown, that at its peak employed 13,000. In 1930 it was closed permanently. At Old Kilpatrick, Napier And Miller shipyard had closed permanently. And in Dumbarton there were two shipyards - Denny, which stayed open, and McMillan, which closed permanently.

"It got to the stage the only contract in the whole district was the Queen Mary, so when it stopped it was appalling. The story went that the day they announced the suspension of the contract, something in the region of 2000 men went to the employment exchange at Kilbowie Road. These are skilled men and in a photograph taken they were all well-dressed chaps, technical people with great skills as well as labouring classes. It was just devastation," says Mr Johnston.

"The tragedy was that it was the last hope for employment and when the contract was suspended that was it, it was just misery and despair. It had never been so bad for shipbuilding on the Clyde."

From those very first plans made in the drawing office at John Brown it was understood that the Queen Mary had to be, quite simply, a magnificent ship. Her competitor, the French Line's Normandie, was being built at the same time and both would battle for the honour of taking the Blue Riband for the fastest North Atlantic crossing, a pivotal accolade for a shipping line in the days before regular air travel.

Extra horse power was built into the Queen Mary and she took the title. The fastest crossing time was three days, 21 hours and 48 minutes, recorded on August 8, 1938 and held for 14 years until it was smashed by the SS United States.

Opulent luxury was the order of the day on board, accommodating 776 in cabin class, 784 in tourist class and 579 in third class; the fabulous Art Deco surroundings of the Queen Mary were beyond dispute. On board a ship renowned for wonderful timber panelling and beautiful veneers, more than 50 different hardwoods featured in the fittings, something that would be unheard of with today's conservation policies. Hundreds of original artworks were commissioned for the best cabins and lounges and acclaimed Glasgow outfitter Rowan And Boden contributed to much of the fittings.

There were swimming pools, ballrooms, restaurants and bars as well as grand salons, elegant sweeping staircases and sumptuous state rooms. Plenty of tales were told over the years of late-night revellers filling the bars and the decadence of formal evening dinners.

The passenger list read like a who's who of the silver screen, from Bob Hope and Fred Astaire to Bing Crosby and Audrey Hepburn. Elizabeth Taylor often travelled with her two poodles, Clark Gable delayed departure in 1948 by 18 minutes because he was busy saying goodbye to his girlfriend and Lynne Redgrave sailed on the ship's final voyage in 1967. During the Second World War, Winston Churchill sailed three times on the ship and the Duke and Duchess Of Windsor, Edward VII and Wallis Simpson called it "their ship" and always booked suite M58 on the main deck.

When the Second World War dawned the Queen Mary was requisitioned as a troop ship, carrying thousands of men around the world. Her instantly recognisable three red funnels and the rest of the superstructure were painted grey, only restored to their former glory after war ended.

Today the ship sits permanently at Long Island, California, and guests can stay on board, although they do not move from the quayside. The glamour and drama of the great Queen has not diminished over the years and is as much a proud reminder of Clyde shipbuilding as always. n

A Shipyard At War: Unseen Photographs From John Brown's, Clydebank by Ian Johnston is published by Seaforth Publishing, priced £30; and Ships For A Nation: The History Of John Brown & Co by the same author is published by West Dunbartonshire Libraries & Museums, priced £27.20.