Shamrock V was the first British yacht to be built to the new J-Class rule. She was commissioned by Sir Thomas Lipton for his fifth America's Cup challenge. Although refitted several times, Shamrock is the only original J-class never to have fallen into dereliction.

The J Class of racing yachts were built to the specifications of Nathanael Herreshoff's Universal Rule. The J Class is considered the apex of the era when the Universal Rule determined eligibility in the America's Cup.