In 1934, Sopwith challenged for the America's Cup. His challenger was Endeavour. She was Charles Nicholson's third J-Class design and he said of her “She will have quite a normal hull… because I have thought it right to suppress possible experimental form, which would be most interesting to try out, but which I have to leave to American designers.” He did, however, produce the most beautiful J-Class and her rig was innovative.


Sopwith experimented with new running backstay strain gauges, which controlled the trim of the mast and used electronic windspeed and direction indicators. It has since been suggested that part of the reason for her failure in the Cup was due to all the gadgets on board. She was matched 83ft 3in on the waterline against Rainbow's 82ft. However, despite being thought to be the best challenger Britain has ever built, she did not win the Cup. Rainbow, which was considered the inferior boat, beat her by four races to two.