A new exhibition on the former mess deck of the 11,553-ton cruiser will help children who are getting to grips with the Britons at War element of the national curriculum to make the imaginative leap. And that presents education officer Sarah Hogben with a dilemma: how far does she go in facing seven to 14-year-olds with the facts of a nightmarish campaign of that war, the Arctic convoys, which ran the gauntlet of German air and sea attacks to carry precious supplies to beleaguered Russia?
Silhouetted against the horizon by the almost round-the-clock light of Arctic summer, which made them perfect targets for U-boat packs and enemy bombers, or battered by Force-10 winter gales and temperatures of -30 LESS THAN F, which could encase a ship in ice almost to the point of capsizing, the men of the "Suicide Run" to Murmansk couldn't win. Eighty-one merchant ships and numerous escorts, with 525 and 2,055 casualties respectively, were the price paid, in Churchill's words, "to keep our Russian allies supplied by all means".
"We had a veteran on board recently who, shown an Aldis signalling lamp, remarked casually that a shipmate had frozen to death operating one," Ms Hogben said. "I sometimes think that we should have men with those experiences sharing them with the children - but then doubts arise."
Plenty of material in the exhibition helps to visualise the scale of heroism and physical hardship involved for Kreigsmarine as well as Royal and Merchant Navy men. Belfast's most formidable adversary was the battlecruiser Scarnhorst from the Norwegian fjord where she had lurked for more than a year - and sailed straight into a trap.
Her commander's plans to attack convoy number JW55B were deciphered by a top-secret Enigma machine, similar to the one on display. The admiralty had time to prepare a battle group comprising the battleship Duke of York (which with its 14-inch guns, could on its own outrange the German ship) the cruiser Norfolk, and a light cruiser "screen", including the Belfast.
In her classroom in the former petty officers' mess, Sarah introduces children - for whom, as she admits, the Battle of North Cape seems as distant as the age of sail - to the men who fought it, through their diaries, letters, and by trying on their kit of duffle coats and thick socks. Invited to pull the white anti-flash balaclavas over their heads they invariably chorus, "Just like Damon Hill!" Sarah is quick to point out that they fuilfilled the same purpose - preventing the hideous burns which could accompany a direct hit.
School parties are made aware that in some cases youngsters not much older than them faced that Christmas of 1943 in stinking, overcrowded quarters with only 21 inches of hammock space per man, and knowing that a well-aimed salvo from Scharnhorst's broadside would at best mean them swimming for their lives in freezing, oil-befouled water where they would have less than five minutes' survival time. Once below decks, amid the tangle of pipes and valves - the only exits being narrow, vertical shafts - it is apparent that survival was almost impossible.
This is brought home poignantly by the diary of Boy Seaman William Crawford, who, when Belfast hit a magnetic mine two months after the outbreak of war and went into dry dock for repairs, joined HMS Hood with many of his shipmates. "Mighty" Hood was sunk in May 1941 by the Bismarck with one shot in her shell magazine and a few weeks later Mrs Crawford received a telegram at her Edinburgh home "regretting that her son was missing". There had been three survivors from a crew of nearly 2,000.
Their deaths hardened the resolve of Belfast's crew for the coming battle, but did not affect their magnanimity to defeated foes, as proved by testimonials signed by the 36 survivors from the German ship - one or two of whom still keep in touch with Belfast's staff - and their beautiful scale model of Scharnhorst, which they donated to the museum.
Their enthusiasm primed by exhibits like Scharnhorst's reserve battle ensign, lumps of a shell from her 11-inch guns which killed 12 men in HMS Norfolk, and the last telegram which the German commander, Admiral Bey, sent to the Fuehrer, "We shall fight to the last shell", children are ready for an audio re-enactment of the battle. As they jostle for their turn on the wooden deck seat from which Vice-Admiral Robert Burnett directed the cruiser's actions, the Tannoy cuts in: "Enemy in sight." (Belfast was the first ship to spot Scharnhorst on her radar.) Then the crump of gunfire is followed by: "She is getting our range. Scharnhorst has turned away at high speed. She is making a run for it."
The commentary explains: "It is up to us to drive her into the arms of the Duke of York, so settle down for a long chase." Belfast's 12 six-inch guns look formidable and the great carousels of shells waiting to be hoist to the turrets could help her hold her own with any opponent - or so one thinks. All that she, along with HMS Sheffield, could do, however, was to act as game drivers and leave the Germans' fate to the massive armament of the Duke of York. With Scharnhorst at bay and badly wounded, the flagship signalled Belfast: "Finish her with torpedoes." The taped commentary ends: "Torpedoes fired," and then we hear, from the sonar operator, "Explosions underwater sir. It looks as though she has gone."
Two of the exhibits speak most eloquently of that last action in Western waters between capital ironclads. A Christmas card from Able Seaman Eddie Gould to his mother, apologising for the delay "as we have been busy sinking the Scharnhorst" and a wallet stuffed with Norwegian Occupation currency and containing a photo of a German seaman, posed for his sweetheart. It was found on one of the 1,600 corpses strewn on the sea or carried down in the blazing hull.
HMS Belfast, Morgan's Lane, Tooley Street, London SE1 2JH. Tel: 0171 407 6434. Groups of 10 or more: child Pounds 1.70 (one teacher admitted free for every 10 pupils). A preliminary planning visit by teachers is free