ABSTRACT
Feedback control mechanisms – that is, systems whose behaviour is modifi ed in some desired manner by manipulating them in response to the system output – have been known since ancient times.1 Modelling them and predicting their behaviour, however, proved to be diffi cult, and became a major problem in the nineteenth century in connection with the control of steam and hydraulic turbines. While major strides were made in this fi eld during the second half of the nineteenth and fi rst half of the twentieth centuries,2 it was during the Second World War that a discipline of feedback control began to emerge, using a range of design and analysis techniques to implement high-performance systems, in particular those for the control of anti-aircraft weapons.3,4 In particular, World War II saw the coming together of engineers from a range of disciplines – electrical and electronic engineering, mechanical engineering, mathematics – and the subsequent realisation that a common framework could be applied to all the various elements of a complex control system in order to achieve the desired result. This approach, later known as ‘systems engineering’, was a major technological breakthrough.
