Fanny = Female Genital Organ (which has expanded from the next example >) & a slang derogatory word for a female.
(comes from a serviceman's vocabulary during the 1st & 2nd World Wars, i.e. "im going out to try &
get myself a Fany")
and the term has developed from there to not just
mean a female, but her actual sexual organs.
(this could be where the
Americans get it from i.e. "im going out to try & get myself some ass (FANY)"
it relates to THE FIRST AID NURSING YEOMANRY (FANY) which was created in 1907 as a first aid link between
front-line fighting units and the field hospitals. (FANY's {Fanny} = the nurses)
During the First World
War, FANYs
ran field hospitals, drove ambulances and set up
soup kitchens and troop canteens, often under highly dangerous conditions.
so therefore were mostly the only female's the sex starved soldiers came into contact with.
see > www.fany.org.uk