The young English scientist joined the Radiophysics Division of the government's Council of Scientific and Industrial Research (CSIR, now CSIRO). Pearcey was aware of recent computer developments in Britain and the US, and in early 1947 he persuaded his superiors to form a small team to develop an experimental program computer.
Pearcey worked on the logical design while his colleague Maston Beard led the electrical engineering. Their computer was developed with only partial knowledge of parallel British and American developments. While Pearcey visited England in late 1948 and inspected the latest projects, by then the logical design of the CSIR machine was essentially complete.
The CSIR Mark 1 ran its first test program in November 1949, making it the fourth stored-program computer in the world. Coming into full operation in 1951, it embodied many features novel at the time and was able to operate more than 500 times faster than the best mechanical calculators.
For five years the team continued to experiment and steadily expand the computer's capabilities, using it to solve a wide range of mathematical problems.
In 1954, Pearcey's bosses decided the Radiophysics Division should concentrate on its major projects in radioastronomy and rain physics. A new home was found for the CSIR Mark 1 in Melbourne, along with a new name - CSIRAC.