T O sail a convoy of more than 50 ships through the icy waters of the Arctic Ocean, battling through the iceberg-ridden seas, constantly chipping ice from the deck of the ship to prevent capsizing, would be hard enough in peacetime.

But the extraordinary Merchant Navy seamen who experienced the infamous Arctic Convoys of World War II, and their Royal Navy escorts, went through all these trials while under constant attack from German U-Boats.

Churchill himself described the convoys as "the worst journey on Earth", but they played a vital role in the war effort by keeping the Soviet Union supplied with food and weapons – and in so doing they kept the Nazi war machine busy maintaining a Russian front.

But 70 years on from the epic series of convoys, which cost the lives of some 3,000 British seamen, a Bristol researcher has spent the last six months coming to terms with the horrors of the survivors' tales.

Pete Vance, senior researcher with Testimony Films, has been hard at work making a new documentary on the convoys to mark the 70th anniversary.

The film, which will be broadcast on the Yesterday channel tomorrow, promises to give viewers an in-depth understanding of the trials facing the seamen, with a series of interviews with surviving veterans.

"There are only about 200 men left who actually experienced these convoys firsthand," Pete explains, as he leads the way to his office on the top floor of a Georgian building in Great George Street.

"It's important to properly document these men's memories of the convoys while we still can. You can read as much as you like about the convoys in the history books, but nothing brings their experiences to life quite as well as hearing the men themselves talking about what they went through."

Pete, who joined Testimony four years ago as a wide-eyed film studies graduate from Exeter University, says he's learnt a lot about the history of the convoys through meeting the men.

"We travelled all over the country to interview six of the surviving seamen – three merchant seamen and three Royal Navy veterans who escorted the supply ships as they tried to dodge the German torpedoes.

"Some of the men's stories were incredibly moving. One man told me how he clambered into a lifeboat after his ship had been torpedoed, only to find his friend climbing in beside him on fire.

"They manage to get the flames put out, but the two men spent four days drifting in the Arctic Ocean before they were rescued, and all he could do for his friend was to ease the pain of the burns a little by handing him a cigarette to smoke every few hours – the man's hands were too badly burnt to hold the cigarette for himself.

"When you hear stories like that, it really brings it home just how traumatic an experience these men went through.

"They were all young guys at the time, in their early 20s – many were still teenagers. But they found themselves as sitting targets for U-Boats in one of the most inhospitable environments on Earth.

"For the documentary, we have been able to uncover a lot of archive film showing the ships covered in ice, with the sailors chipping away at it to try to keep the weight of the ship balanced.

"But the ice formed as quickly as they could chip it off. One of the most common jokes the sailors would play on the junior seamen was to ask them to fetch a hot cup of cocoa – they knew that by the time they had come back from the galley with the drink, it would have frozen solid.

"That's how cold it was. It really is hard to imagine.

"If the sailors touched the metalwork of the ship for just a moment, they would find the skin on their hands attached to the cold metal.

"These guys were going through hell even before the Germans started torpedoing them."

One man who remembers just how harsh conditions onboard the ships were, is merchant navy veteran Tony Winterburn.

Tony, 86, from Burnham-on-Sea, was a radio operator on the ss Empire Portia.

He joined the ship on his 17th birthday, and within just a few weeks found himself heading out on the toughest sea voyage in history.

"We didn't know of course," he says. "When I got on the ship at Liverpool, I could see we were being loaded with munitions, but I had no idea of our destination until we were well on our way around the north of Scotland.

"But as a teenager fear doesn't come into it. The only thing I was afraid of was that I might miss something – I spent a lot of my free time on the bridge, because I was fascinated to see the convoy working in formation.

"It was dark for the entire voyage – this was the Arctic winter of course – but the cold was a dry cold. It was -20°C, but it wasn't a damp cold that cut through you – it wasn't too uncomfortable as long as you didn't expose your skin or touch any of the metalwork on the outside of the ship."

Tony's convoy, code-named JW52, which left the UK in December 1942, was one of the few that reached Murmansk without any ships lost.

"We were very lucky," he says. "The U-boats were there, but they couldn't keep up with us when they were submerged, and our Royal Naval escort was strong enough to be able to stop them surfacing and catching us up.

"There were torpedo bombers trying to get us along the route, too – German planes taking off from the coast of occupied Norway, but they were also unable to hit any of our ships during the voyage. It was miraculous really."

However the crew's luck ran out when they reached Russia.

"We had discharged our cargo, and loaded the ship up with timber and cotton to take back to Britain," he recalls. "We were waiting in an inlet for the convoy to reassemble for the journey back, when a German ME109 came over and bombed the ship – damaging the hull and setting fire to the cargo, although incredibly none of the crew were injured." It did however mean a two-month wait for Tony and the crew in a village outside the bomb-ravaged city.

"There was nothing we could do but wait for the ship to be repaired," he says. "It wasn't until November 1943 that we were finally able to make the return journey back through the Arctic."

Veterans of the Arctic Convoys have never been awarded a campaign medal for their service in the far north, and while the Arctic Convoy Association continues to campaign for a medal, Tony says he is not too concerned by the issue.

"I've always said if you have to twist the Government's arm to get a medal, then it's probably not worth having."

● Arctic Convoys is broadcast on the Yesterday channel tomorrow at 10pm.