Skinner & Stacke 1922, p. 6. Skinner, H. T.; Stacke, H. Fitz M. (1922). Principal Events 1914–1918. History of the Great War Based on Official Documents by Direction of the Historical Section of the Committee of Imperial Defence. London: HMSO. OCLC17673086. Retrieved 7 February 2014 – via the Internet Archive.
Skinner & Stacke 1922, p. 6. Skinner, H. T.; Stacke, H. Fitz M. (1922). Principal Events 1914–1918. History of the Great War Based on Official Documents by Direction of the Historical Section of the Committee of Imperial Defence. London: HMSO. OCLC17673086. Retrieved 7 February 2014 – via the Internet Archive.