Evidence has emerged of a wartime blunder that resulted in millions of pounds of Russian bullion, supposedly bound for America, being lost in the river Clyde. The gold and silver bars had been loaded in Murmansk onto a former Irish Sea ferry, converted into a battle cruiser with her superstructure stripped to take part in a dangerous Arctic convoy. The bullion was to pay the Americans for arms shipped to Russia during one of the most crucial stages of the Second World War. Scroll down for video . The bullion was loaded onto the HMS Ulster Queen (pictured) in 1942 and was being transferred to the U.S. as payment for weapons when the case of precious metals was lost overboard . The former ferry, HMS Ulster Queen, arrived in Greenock in November 1942, after 13 days at sea and two ships sunk by German U-boats. But as a delicate operation began to transfer the cases of treasure onto a waiting boat, one slipped and fell into the muddy waters. Such a veil of secrecy existed over the whole operation it is not known if it was ever recovered. In fact, the incident has only come to light thanks to a secret diary kept by one of the Ulster Queen's engineers, and now revealed by his daughter for the first time in a new book. Edinburgh man Leonard H. Thomas served on the Ulster Queen on four convoys to and from Murmansk and Archangel in Russia's extreme northwest. Mr Thomas had got into the habit of keeping copious notes and sketches during his pre-war role as a crewman on the research ship RRS Discovery II in the Southern Ocean. He had joined the Discovery as a 17-year-old in his native Portsmouth. He continued his writings on the Convoys - but aware that should any of his diaries be discovered he would be in serious trouble, he wrote in code and secreted them well. Before he died in 2000, aged 88, he transcribed some of them into four A4 journals, which his daughter, Leona Thomas, has now edited into a book. Edinburgh man Leonard H. Thomas served on the Ulster Queen on four convoys to and from Russia's extreme northwest . Leona, 61, a retired school teacher, said yesterday: 'The story about the Russian bullion is fascinating. It must be documented somewhere, but I have never been able to find out what happened afterwards.' According to her father's notes, there had been 'a peculiar silence all through the ship' as she was loaded in Russia. No one was allowed on deck, no one was allowed along the alleyways forward of the engine room, and no one off the mess decks unless they were on watch. Mr Thomas recorded: 'No scuttles [were] allowed to be opened, but someone got a gleek out and saw mighty big steam locomotives smothered in soldiers, up and down the cleared area of the track, hundreds of them, all with rifles and many with Tommy guns. 'Our guards lined the deck, we later heard, either side of a small derrick which handled the paravanes [mine detectors]. A huge, dark wagon was coaxed, nudged, and jogged until the derrick's fall was hanging vertically and a rope net was placed on the ground. 'Officers approached the wagon and examined locks and bolts [with] armed troops literally surrounding it. Then began the laborious manual exercise of [unloading] what looked like ammunition boxes, which required two men to lift. 'Surely this wasn't small arms ammunition! Not with our own guards and hundreds of troops watching it loaded into us. It certainly was not. It was bullion! 'Two boxes were enough to load the sling and up they went, deposited on our deck, from where each one was slid and lowered down into the 'B Gun' magazine, never out of sight of at least one officer. 'This was the arrangement so that the millions could be spent in the USA to arm the Russians.' 'Then into the Wardroom [went the] harassed officials, who, we heard, lashed into the whisky "as if it were free." Probably, with all that off their hands, they could afford to.' Once back in the Clyde, after 'a fast run down the Minches', calamity was to come, however. Mr Thomas wrote: 'It was very late when we saw the welcoming but shaded lights of the Boom Control vessels, hauling left and right to usher us through the widening but regulated aperture, and suddenly the serenity of approaching a hallowed anchorage and being met by a small but important armada and a lighter. 'For the next hour it was cloak-and-dagger stuff again, no one allowed on the upper deck forward of the Wardroom or on the working alleyways. We heard that troops and all sorts were organised to receive the bullion from where it had been man-handled onto the upper deck. 'The paravane derrick was reeved [threaded] and a wire was taken with snatch blocks to a winch. The first two boxes were slung with a hemp rope-sling. Mr Thomas, who died in 2000 aged 88, pictured with his late wife Louie in 1996 . 'In the shaded lights were many officials, officers, men in good suits, bayonets, torches, clipboards, tarpaulins, surreptitious smokers, but nary an onlooker. 'Our Captain anxiously peered over the port wing of the bridge, his nose barely over the canvas dodger, to observe the last rites of the Russian bullion. 'And then it happened. The first boxes, two in number, were being hauled toward the lighter, and who knows what happened, but one slipped and fell with a resounding thump and a splash into the Clyde. 'I was told on good authority that it was nothing so much as resembling a H. M. Bateman cartoon. Needless to say, all were to blame according to what was imparted as a result of this shocking affair. 'The rest was capably transferred to a lighter, various bits of paper signed, exchanged, and pocketed, and a tug chuffed up to pull the lighter clear.' Written in the diaries left for his daughter, Mr Thomas said: 'I was thankful to keep all these years, the actual daily scroll of some of the harrowing times I found myself in, especially the runs in the arctic waters so fraught with danger, both man-made and that of nature.' Leona said of the gold: 'Who knows, it may still be there.' Mr Thomas wrote in his diary how the crew of the Ulster Queen had hoped their ship would be chosen to steam straight for America, so they could 'live it up' for a few days before returning to war-torn Europe. In the end, the decision was apparently made to off-load the cargo in the Clyde, for eventual transfer to another vessel for the Atlantic crossing. The HMS Ulster Queen pictured in her pre-war days as an Irish Sea ferry. She was later converted into a battle cruiser with her superstructure stripped .
Edinburgh engineer detailed how bullion was lost during secret mission . Leonard H. Thomas served on HMS Ulster Queen during Arctic Convoys . His secret diaries reveal a crate of bullion was lost while being transferred . Mr Thomas wrote it fell into river Clyde while being moved to another ship . The mission was so secretive it is not known if bullion was ever recovered .