In 1940, when she heard a BBC radio call for German speakers to join the W.R.N.S. (Women's Royal Naval Service) she felt that this would be a good use of her skills. She spent time in Dover Castle as C.P.O. Telegraphist, Special Duties, listening to communications between E-boats (enemy motor torpedo boats) in the English Channel during the threatened German invasion, and also served in this capacity in Portland Bill,

on England's south coast, and in Bone, Algeria. She met other young British servicemen and women on her train and bus journeys to and from assignments. Some friends made during the war years kept in touch long afterwards. On one occasion she left her German grammar book on a bus in England. When the book was discovered it triggered a minor spy scare and Rosemary had to explain herself to the authorities.