Frederick William Lanchester, Aircraft in Warfare — Chapter XVI (1916)
“ Thus a machine may be unfit for service either because it is, according to some accepted definition, worn out and incapable of repair, or because it is obsolete in design. In some cases obsolescence may be absolute, as when a design is so out of date that by comparison with the best available it is to be considered unsafe or uneconomical; in this case it is only fit to be destroyed; or its obsolescence may be relative, as when it is out-classed by the machines of corresponding type in the service of some neighbouring Power ”
