The weight goals for both F-111 versions proved to be overly optimistic.
Excessive weight plagued the F-111B throughout its development.
The prototypes were far over the requirement weight.
Design efforts reduced airframe weight but were offset by the addition of the escape capsule.
The additional weight made the aircraft underpowered.
Lift was improved by changes to the wing control surfaces.
A higher thrust version of the engine was planned.
During the congressional hearings for the aircraft, Vice Admiral Thomas F. Connolly, then Deputy Chief of Naval Operations for Air Warfare, responded to a question from Senator John C. Stennis as to whether a more powerful engine would cure the aircraft's woes, saying, "There isn't enough power in all Christendom to make that airplane what we want!"

With the F-111B program in distress, Grumman began studying improvements and alternatives.
In 1966, the Navy awarded Grumman a contract to begin studying advanced fighter designs.
Grumman narrowed down these designs to its Model 303 design.
With this the F-111B's end appeared near by mid-1967.
By May 1968 both Armed Services committees of Congress voted not to fund production and in July 1968 the DoD ordered work stopped on F-111B. A total of seven F-111Bs were delivered by February 1969.
The weight goals for both F-111 versions proved to be overly optimistic. Excessive weight plagued the F-111B throughout its development. The prototypes were far over the requirement weight. Design efforts reduced airframe weight but were offset by the addition of the escape capsule. The additional weight made the aircraft underpowered. Lift was improved by changes to the wing control surfaces. A higher thrust version of the engine was planned. During the congressional hearings for the aircraft, Vice Admiral Thomas F. Connolly, then Deputy Chief of Naval Operations for Air Warfare, responded to a question from Senator John C. Stennis as to whether a more powerful engine would cure the aircraft's woes, saying, "There isn't enough power in all Christendom to make that airplane what we want!"
With the F-111B program in distress, Grumman began studying improvements and alternatives. In 1966, the Navy awarded Grumman a contract to begin studying advanced fighter designs. Grumman narrowed down these designs to its Model 303 design. With this the F-111B's end appeared near by mid-1967. By May 1968 both Armed Services committees of Congress voted not to fund production and in July 1968 the DoD ordered work stopped on F-111B. A total of seven F-111Bs were delivered by February 1969.
General Dynamics–Grumman F-111B