Chauncy Batho Dashwood Strettell was born on 6 August 1881, the eldest son of Lieutenant-Colonel Arnold Dashwood Strettell (1845–1933), of Hythe in Kent, and his wife Harriette Elizabeth "née" Batho (died 1884), daughter of William Fothergill Batho (1828–1886), a civil engineer, of Surbiton in Surrey. He had a younger brother, Arnold William Cunninghame (1884–1888), and two half-siblings by his father's second marriage to Hortense Augusta (died 1951), daughter of Francis Levien, secretary to the London Stock Exchange: Doris Eileen (born 1892) and Colonel Eric Francis Dashwood, (1894–1970). His father entered the Indian Army in 1862, serving successively with the Connaught Rangers and the 190th Regiment. He fought in the Abyssinian Campaign, before working for a year in the Bengal staff Corps. He was in the Kurram Column 1878–79, the Waziri Expedition of 1881 and the Takht Sulliman Expedition of 1891.