This movie's title is taken from the expression "Hornet's Nest" meaning a violent or gravely contentious situation. In the film's case, this is relates to the the dangerous and difficult mission to blow up a dam protected by the Nazis. The expression is derived from the habitation for wasps or hornets, something which if disturbed can become a situation that presents itself with difficulty to the disturber.
The credited director in English-language prints is Phil Karlson, but Italian prints list Karlson and Franco Cirino as co-directors. Cirino was a second-unit director who worked with American directors on films made in Italy and the Mediterranean. He also occasionally worked as an actor in them.
A year before this film was made, Sylva Koscina had appeared in another World War II movie, The Battle of Neretva (1969), aka "The Battle of Neretva", which was filmed in her home country of Yugoslavia.