This was Hitachi's first transistor computer. Development began around May 1958, with guidance from the Electrotechnical Laboratory (which had completed the ETL Mark IV). Whereas the purpose of the HIPAC MK-1 was technical computation, this machine was oriented toward business processing. While using the basic circuits of the ETL Mark IV, it expanded the word length to signed 12 digits, and used the paired order system for incorporating 2 instructions into one word. It also had innovations like overflow detection and partial simultaneous operation of input/output. The magnetic drum was designed to be the best available at the time, with a high speed of 12,000RPM and a capacity of 1,960 words.
In contrast with the parametron HIPAC, this machine was called the HITAC (Hitachi Transistor Automatic Computer) 301. It was completed in April 1959, and delivered to the Japan Electronic Industry Development Association. This was the first machine under the HITAC brand, which continues to this day.