Italian submarines and deniable attacks in the Spanish Civil War

Was Italian responsibility for submarine attacks during the Spanish Civil War ever proved?

The evidence convinced those involved, but governments avoided publicly accusing Italy because they feared the consequences for the strategic balance and their rearmament programmes.

The evidence convinced the governments involved that Italian submarines were responsible for the attacks. Publicly accusing Italy risked upsetting the wider strategic balance. Rearmament was the immediate priority, and officials wanted to avoid a confrontation that threatened it. Private confidence in responsibility therefore coexisted with diplomatic restraint.