How Nelson's torpedoes could be aimed

What does it mean that the Nelson class had torpedoes that could turn?

The 24.5-inch torpedoes could steer through a limited angle after launch, allowing the fixed installation to aim at a target.

The tubes did not need to be trained like a destroyer's deck mounting to influence the attack direction. The torpedo itself could turn within a restricted envelope. This allowed the crew to aim at a target rather than accept only the exact straight line of the hull-mounted tube. The capability remained limited, but it made the capital ship's underwater armament more deliberate than a simple fixed shot.