Dear Francesco,

A submarine could be mined without leaving a lot of traces on the water. See the mining of HMS TRIUMPH on 26 December 1939, It was a miracle that she survived. A smaller submarine would not, this is why one cannot rule out completely a mining (for HMS UPHOLDER, HMS URGE or even the larger HMS ODIN).

In the case of HMS ODIN, I would point out that after the BALENO's attack, the destroyer DARDO reported missed by a torpedo at 2338 hours/16 June 1940 in position 40°01' N, 17°23' E when on an antisubmarine sweep with destroyers SAETTA, FRECCIA and STRALE. This was about 20 miles from BALENO's attack and might mean that HMS ODIN had survived the attack of 14 June. At 0042/17 June, it was the turn of FRECCIA to report a torpedo track.
Finally at 0127/17 June, SAETTA was narrowly missed by two torpedoes in 39°23' N, 17°40' E.

If one believes that one of these torpedo attacks was genuine, if not all, then it would mean this was the work of HMS ODIN as this was in her patrol area and there were no other British submarines in this zone. Since no oil or debris was observed, then the submarine probably survived perhaps to be mined later.

It is also not impossible that all three "attacks" were bogus and porpoises were mistaken for torpedoes, not unusual in the first days of the war when everyone was a bit nervous. This could mean that BALENO may have sunk HMS ODIN.

I do not claim to have a definite answer and can only point to a few possibilities.

All the best,

Platon