Complex sentence: When first seen in reconnaissance photography, the large wing planform suggested an enormous and highly maneuverable fighter, at a time when U.S. design theories were also evolving towards higher maneuverability due to combat performance in the Vietnam War.
Split into simpler sentences: When first seen in reconnaissance photography, the large wing planform suggested an enormous and highly maneuverable fighter. This was during a period of time when U.S. design theories were also evolving towards higher maneuverability due to combat performance in the Vietnam War.