Constance Shacklock OBE (1913–1999) was an English contralto. After more than a decade of roles with the Covent Garden Opera Company, with other companies and on the concert stage, Shacklock performed for six years in The Sound of Music in London as the Mother Abbess. She taught singing at the Royal Academy of Music from 1968 to 1978. 　　Shacklock was born in Sherwood, Nottinghamshire, and trained at the Royal Academy of Music. Her career took off after she was recruited in 1946 to the new Covent Garden Opera Company. Her first Covent Garden appearance was in Purcell's masque The Fairy-Queen. She remained with the company for a decade, beginning with small roles such as Mercedes in Carmen and moving up to leading parts including Carmen, Octavian (Der Rosenkavalier), Marina (Boris Godunov), Magdalene (Die Meistersinger), and Mrs Sedley (Peter Grimes). In 1948 she was cast as Brangane in Tristan and Isolde alongside the celebrated Norwegian soprano, Kirsten Flagstad. In 1953 she shared the title role of Britten's Gloriana with Joan Cross. 　　Away from Covent Garden, Shacklock appeared in opera in Berlin with Erich Kleiber, and sang in oratorio, notably as the angel in The Dream of Gerontius with Sir John Barbirolli. She was also a regular at Last Night of the Proms with Sir Malcolm Sargent, celebrated for her singing of Rule, Britannia!.She also performed in Argentina, in die Rosenkavalier with Birgit Nilsson and die Marschallin.