Brigadier Oswald "Jasper" Harker (1886–1968) replaced Sir Vernon Kell as Director of the Security Service in June 1940.

Harker's career began in the Indian Police, for which he worked for fourteen years. He rose to become deputy commissioner at Bombay before being invalided home in 1919. He joined the Service in 1920 on loan from the India Office and in due course became the head of the Service's "B" division, which was responsible for 'investigations and inquiries'.

He was replaced by Sir David Petrie in 1941 but stayed on as the Service's new Deputy Director General. He retired in 1946.