This is the powerful story of the U-boat wars, recreated from the experiences of German survivors. The drama and excitement of it all is more than matched by the constant, numbing danger, unimaginable to anyone who has not lain silent and freezing, facing death beneath the waves in a trapped submarine under attack. All this is set in the context of changing U-boat strategy, and highlights not just the faults that were to cause the U-boats, in the end, to fail, but the extraordinary bravery of the men who sailed in them, seventy per cent of whom died.