The Cosmotron was a particle accelerator, specifically a proton synchrotron, at Brookhaven National Laboratory. Its construction was approved by the U.S. Atomic Energy Commission in 1948, it reached its full energy in 1953, and it continued running until 1968. It was the first particle accelerator to impart kinetic energy in the range of GeV to a single particle, accelerating protons to 3.3 GeV. It was also the first accelerator to allow the extraction of the particle beam for experiments located physically outside the accelerator. It was used to observe a number of mesons previously seen only in cosmic rays, and to make the first discoveries of heavy, unstable particles (called V particles at the time).