Is the Pegasus hydrofoil a Dog Boat successor?

Was the Pegasus hydrofoil the natural progression of the small PT boat?

Only partly. It extended high-speed planing ideas, but it is closer to the Schnellboot tradition because a hydrofoil cannot easily carry the Dog Boat's adaptable heavy weapons load.

Pegasus carried the pursuit of speed beyond conventional planing hulls, so it belongs to the broad fast-attack-craft lineage. A hydrofoil is nevertheless closer to the Schnellboot approach than to the Fairmile D. Hydrofoil performance depends on tight weight control and mechanically complex lifting surfaces. The Dog Boat's identity rested on accepting less extreme speed in exchange for structural strength, heavy weapons, and repeated adaptation to new roles.