Sovereign (sail number K-12) was the unsuccessful challenger of the 1964 America's Cup for the Royal Thames Yacht Club.

This was the second post-war 12-metre yacht to be designed by David Boyd and built at Alexander Robertson & Sons, the first one being Sceptre.

Sovereign lost 4–0 to defender Constellation of the New York Yacht Club.

Many members at that time thought that for a club that was founded in 1775 and participated in America's Cup since 1870 to withdraw from the tournament completely was an embarrassment.

The boatyard that built the yacht was sold by the Robertson family, who owned it since its foundation in 1876, one year after the race, essentially ending wooden boatbuilding there.