SWAC

The Standards Western Automatic Computer was the National Bureau of Standards' second machine, built at the Institute for Numerical Analysis in Los Angeles and finished in August 1950. Where SEAC chose safe delay lines, designer Harry Huskey — a veteran of both ENIAC and Turing's Pilot ACE — bet on Williams tubes, an electrostatic cathode-ray memory that was faster but far more temperamental. For a time the gamble made SWAC the fastest computer anywhere.

With only 256 words of memory and no hardware multiplier, SWAC was nonetheless a workhorse for numerical analysts. In 1952 Raphael Robinson set it hunting Mersenne primes, and it found five new ones in a single day — the first ever discovered by computer. It was scrapped in 1967.