Confidential papers were retireved by the boarding party prior to the sub's sinking, but definitely NOT an Enigma machine, for one simple reason: The Italian Navy did not start using enigma until February of 1941 and then only at the insistence of the German High Command.
Until that time, Italy had been using a Swedish coding system which the British, ironically, had NOT been able to break. As soon as Enigma came into play.... the results are sadly well known.
Regards, Brian