Cromwell is the launch director at McKinley Rocket Base in Assignment: Earth, in charge of sending an orbital nuclear weapons platform into space in 1968.
Cromwell is a twentieth-century American official in the Original Series episode Assignment: Earth. He directs operations at McKinley Rocket Base, where the United States is about to launch an orbital nuclear warhead platform in answer to a similar move by a rival power.
He runs the countdown from mission control, unaware that the mysterious agent Gary Seven has slipped on to the gantry to tamper with the rocket and that Kirk and Spock, visitors from the future, are also inside his base.
Kirk and Spock are caught and held in the control room, where Cromwell and his team watch in alarm as the rocket goes off course with its warhead armed. It finally detonates harmlessly high above the ground, the scare Seven intended in order to frighten the powers away from weapons in orbit.