Keeping aerial torpedoes shallow at Taranto

What made shallow-running aerial torpedoes difficult, and how did the British manage it?

British torpedoes used a tension wire and fins to control the drop and produce a shallow water entry.

The difficulty was controlling the torpedo's depth and direction as it entered the water. A tension wire progressively unwound from the nose, working with fins to keep the weapon level during the drop. The intended entry was a shallow belly flop. Japanese study of Taranto is said to have noticed the visible wooden fins while missing the importance of the less obvious wire. The comparison with torpedoes diving too deep at Pearl Harbor illustrates the argument about water-entry control.