Found this excerpt while reading about this incident.

"The 3 survivors were lookouts on the ship's mast

Although you are bang on with the number of casualties, which is often wrong (due to official figures having become very ingrained in the public consciousness before being amended), you're not quite right on where the three survivors were - although two were indeed on or near the compass platform (though not 'blown clear'), the third was a gunner elsewhere on the ship.

The three survivors were:

William Dundas:

He was at his post on the Compass Platform when Hood was fatally struck by Bismarck on 24th May 1941. He was able to escape by kicking out one of the starboard side windows and swimming away. He demonstrated great skill and bravery during the sinking and afterwards. This was demonstrated by his tireless efforts to keep the other two survivors awake/coherent and alive until help could arrive.

Bob Tilburn:

When Hood and Prince of Wales intercepted the German warships Bismarck and Prinz Eugen on the morning of 24 May 1941, Bob was at his station on one of the 4" guns on the port (disengaged) side of the ship.

Ted Briggs:

Briggs was to recall: "A blinding flash swept around the outside of the compass platform. I found myself being lifted off my feet and dumped head-first on the deck." For Briggs, this was a moment of extreme terror. Since his first sighting of the mighty Hood as a boy of 12, he had always wanted to join it. Now, after two wonderful years, his home, his ship, was disintegrating. There was no order to abandon ship, but everyone was trying to get out, and to his amazement, the Flag Officer, seeing the youthful Briggs, gave way to him – an action which saved Briggs' life.

With the ship almost on its side, Briggs climbed down a ladder. As the freezing sea hit his legs, he took off his tin hat, gas mask and anti-flash gear. The ship lurched and he was sucked under – but a sudden explosive release of gas blasted him back to the surface. He recalled, "I could hear what sounded like the hissing of a hundred serpents, so I turned, and 50 yards away I could see the bows of the Hood, standing vertical in the sea."