So thats why the Mustang and Spitfire have those neat rounded wingtips.
Actually the Spitfire has a wing that was truly elliptical in plan view. Very hard to manufacture, with compound curvature on the skin and highly variable chord length. However, very maneuverable, and, with low drag & a big engine, able to accelerate rapidly at low speed and, following a tight turn, when the g load was relaxed. In the terms of energy maneuverability as later developed by Col John Boyd in the early 1970s , the Spitfire was unmatched.
The Mustang represented a later generation in wing design with less camber and a thinner wing for better performance at higher airspeed. Unusually, it combined maneuverability with long range & high payload. Not so successful at first, but unbeatable after it was fitted with the higher power Merlin engine.
Actually rounded wingtips and the little winglets you can see sticking up from the wingtips of modern airliners have the same function - to reduce the energy lost in the trailing wingtip vortices.
The flow over a wing can be represented as a combination of linear flow and a circular vortex flowing over and under the wing. It turns out that the lift is proportional to the product of airspeed the strength of the vortex (or the line integral of circulating relative airflow on any circular path around the airfoil. This vortex is real, and when an airliner rotates quickly at takeoff it sheds an opposite vortex which stays behind on the runway. On a hot dusty day at a Southwestern airport, you can actually see the standing shed vortex behind the aircraft. That's why small aircraft aren't allowed to land or takeoff for a few minutes behind a "heavy" .