There was a study done on kids born during and just after the Blitz/Battle of Britain. The massive stress from the bombings massively increased cortisol levels in mothers and fetuses. Cortisol acts as sort of an anti-androgen.
The increased cortisol affected the way the male baby brains developed and they found much higher incidence of male homosexuality.
Difficult thing to study, but they hypothesize that throwing off testosterone interaction with fetal brains during critical development period feminized their brains.