ISABELLE, a particle collider at Brookhaven National Lab. It was supposed to find the W and Z bosons through high-luminosity proton-proton collisions, but while the goals of the project were reasonable, the development of the necessary magnets was plagued with problems that weren't fixed until the European SPS had already found the W and Z, leaving ISABELLE with no clear rationale and leading it to be cancelled shortly thereafter in favor of the Superconducting Super Collider.
Of course, SSC was itself a failed megaproject...
(More positively, the civil engineering work done for ISABELLE was reused for the Relativistic Heavy Ion Collider, which has been highly successful, and probably more useful than ISABELLE itself would have been)