Why a teardrop hull was not a universal wartime answer

How much would early teardrop-hull submarines or homing torpedoes change World War II?

Less than it may seem: wartime submarines relied heavily on surface operation, and both hull changes and homing torpedoes bring significant operational trade-offs or countermeasures.

A modern submarine differs from the submersible torpedo boats used in the world wars. A teardrop hull improves underwater performance but gives up surface stability. Wartime boats spent much of their time travelling on the surface because they could move faster and more easily there. Homing torpedoes would add danger, but opponents could still develop countermeasures.