Its construction was overseen by Oliver Standingford, Raymond Thompson and David Caminer of J. Lyons and Co. LEO I ran its first business application in 1951.

In 1947, two of its senior managers, Oliver Standingford and Raymond Thompson, were sent to the United States to look at new business methods developed during World War II.

They also learned from Goldstine that, back in the UK, Douglas Hartree and Maurice Wilkes were actually building another such machine, the pioneering EDSAC computer, at the University of Cambridge.

[1] On their return to the UK, Standingford and Thompson visited Hartree and Wilkes in Cambridge and were favourably impressed with their technical expertise and vision.

On the recommendation of Wilkes, Lyons recruited John Pinkerton, a radar engineer and research student at Cambridge, as team leader for the project.

[4] The first business application to be run on LEO was Bakery Valuations, which computed the costs of ingredients used in bread and cakes.

Its ultrasonic delay-line memory based on tanks of mercury, with 2K (2048) 35-bit words (i.e., 83⁄4 kilobytes), was four times as large as that of EDSAC.

[16] Lyons used LEO I initially for valuation jobs, but its role was extended to include payroll, inventory, and so on.

One of its early tasks was the elaboration of daily orders, which were phoned in every afternoon by the shops and used to calculate the overnight production requirements, assembly instructions, delivery schedules, invoices, costings, and management reports.

The first LEO III was completed in 1961; it was a solid-state machine with a 13.2 μs cycle time ferrite core memory.

[21] One of the features that LEO III shared with many computers of the day was a loudspeaker connected to the central processor via a divide-by-100 circuit and an amplifier which enabled operators to tell whether a program was looping by the distinctive sound it made.

[22] Another quirk was that many intermittent faults were due to faulty connectors and could be temporarily fixed by briskly strumming the card handles.