This book is a study of how scientific computation developed in British universities, the scientific civil service, and the armed services during the period 1900-1950. It describes the emergence of computing laboratories in Britain, along with the machines and personalities involved.British computational work is examined from an organizational perspective and the concept of centralized computing power is discussed. Computing methods used up to the 1950s ranged from the use of mathematical tables, via slide rules and other mathematical instruments, to desk calculating machines, accounting machines, differential analysers, and early computers.