William M. Jefferies was a Human Starfleet admiral in the 2230s and 2240s. He, along with Captain Robert April, was a key supporter of the development of the Constitution-class of starship. Jefferies supervised the construction of the USS Constitution at the San Francisco Fleet Yards. In 2244, Jefferies took the Constitution out of drydock and raced to the Donatu system to take part in the Battle of Donatu V. (TOS - Errand of Vengeance novel: Killing Blow)