One single private soldier, and we would take good care that he was killed.
Source, in full
Response to a question of Henry Wilson regarding a possible German invasion of Belgium: "What would you say was the smallest British military force that would be of any practical assistance to you in the event of a contest such as we have been considering?" (14 January 1910 or possibly later) quoted in Field-Marshal Sir Henry Wilson: His Life and Diaries (1927) by Charles Callwell, pp. 78–79
Notes from Wikiquote
Shorter variant (citing Callwell) in The Guns of August (1962) by Barbara Tuchman, p. 49 | Longer version of Foch's answer to Wilson in Britain and the War, A French Indictment (written 1921–1922, published 1928) by General Huguet, translated by Captain H. Cotton Minchin, p. 26: "After all it doesn't matter what you send us, we only ask for one corporal and four men, but they must be there right at the start. You will give them to me and I promise to do my utmost to get them killed. From that moment I will be at ease since I know that England will follow them as one man!"