On 4 May 1971, four home-made bombs were found in the woods adjoining the school. The authorities suspected that these belonged to the far left militant group known as Angry Brigade. 1972 witnessed Chislehurst and Sidcup's first school trip outside Europe, as 150 boys traveled to New York City. Soon after, the wearing of caps as part of the school uniform was abolished. Links were established between Chis and Sid and the nearby Marlborough Special School for children with special needs, while in 1974 the school's literary society secured Kenneth Williams to speak to them. The first girls arrived at the school in September 1973, representing the sixty female pupils who had the highest test scores from the local primary system. Accordingly, the term "for Boys" was removed from the school's name, while hockey and netball were introduced as sports for the girls to play. Some resentment arose however over the issue of punishment; while boys were still exposed to corporal punishment in the form of caning and (unofficial) slapping, girls were exempt from these measures.