Presumably authentic WW2-era rules for playing through the Richmond (London) country club golf course.

German aircraft from Norway would fly on missions to northern England; because of the icy weather conditions, the barrels of their guns had a small dab of wax to protect them. As they crossed the coast, they would clear their guns by firing a few rounds at the golf courses. Golfers were urged to take cover.

(Source: thedailywhat)