The statement that US 27, Enterprise (Olin Stephens, designer) was the only American Twelve Metre built in aluminum is incorrect. The first aluminum Twelves were built for the 1974 Cup. They were US 25 Mariner (Britton Chance design, built by Derecktor's. Possibly the only slow design Chance ever did.), then US 26 Courageous (Olin Stephens, built by Minneford's. Cup winner 1974 and 1977) As fast as Courageous was, she narrowly defeated 1967/1970 Cup winner Intrepid (built in traditional carvel planked wood) for the right to defend the 1974 contest. For the 1977 defense trials, not only Courageous and Enterprise participated, but also another aluminum Twelve designed by Ted Hood, Independence. (Starting with Independence, I'm fuzzy at best about sail numnbers) For 1980, an American syndicate built Freedom and Magic in aluminum as well as at least one other experimental design, all for Dennis Conner. Independence was stripped down to her keel and rebuilt as Clipper. (David Pedrick, designer)  
 In 1983, Dennis Conner again built a fleet of Twelves, all in aluminum, to fight for the right to defend, settling on Liberty. (Sorry, Johann, I don't remember how to spell your last name). Also, David Pedrick had Defender built to his design.  
 It got really crazy for 1987 in Freemantle. Dennis Conner had no less than three Twelves built for him, settling on Stars and Stripes '87 (US 55) to race. She won the Cup back for America under Dennis' hand. Buddy Melges built Heart of America, Gary Mull designed Evoluton and Revolution (the last Twelve built to the Grand Prix version of the International Rule), sailed by Tom Blackaller. The America II syndicate built two Twelves named after the yacht that started this all, the schooner America (Sail numbers US 44 and US 46, the latter of whch played "Geronimo" in the movie "Wind") I think that another American Twelve was campaigned by Rod Davis, but I'm vague about the details. Throughout all of these years, Courageous was updated and campaigned, being the grand dame of the aluminum Twelve fleet. 
 Please forgive any omissions. This is all off the top of my head. 
 John