The tests were initially developed for research purposes. Because of their independence of language and reading and writing skills, and the simplicity of their use and interpretation, they quickly found widespread practical application. For example, all entrants to the British armed forces from 1942 onwards took a twenty-minute version of the SPM, and potential officers took a specially adapted version as part of British War Office Selection Boards. The routine administration of what became the Standard Progressive Matrices to all entrants (conscripts) to many military services throughout the world (including the Soviet Union) continued at least until the present century. It was by bringing together these data that James R. Flynn was able to place the intergenerational increase in scores beyond reasonable doubt. Flynn's path-breaking publications on IQ gains around the world have led to the phenomenon of the gains being known as the Flynn effect. Among Robert L. Thorndike and other researchers who preceded Flynn in finding evidence of IQ score gains was John Raven, reporting on studies with the RPM.