The XII MAS commenced operations on June 25, 1942, making reconnaissance sweeps across the lake, landing observers behind Soviet lines, and searching for submarines. On July 25, 1942,
MAS 526 was damaged in an accident, and was temporarily put out of action. On the night of August 14–15, 1942,
MAS 527 and
MAS 528 intercepted a force of three Soviet gunboats (according to some sources, only one
MAS 527 participated in the action); after an exchange of fire the MAS closed in and launched torpedoes, sinking one of the gunboats (in reality, not a single Soviet warship was lost in this action; according to Soviet sources, the gunboats and , and the patrol boats , and participated in this action on the Soviet side; one 's
Red Fleet man was wounded by enemy fire; on October 22, 1942, both of these Soviet gunboats participated in an
operation to defend Sukho Island). on Lake Ladoga in the summer of 1942 On the night of August 27–28, 1942,
MAS 527 encountered a Soviet convoy consisting of two tugs pulling a train of barges, escorted by a third tug.
MAS 527 shadowed this group and summoned help, and with the arrival of
MAS 528 attacked with torpedoes, causing the barge train to blow up (according to some sources,
MAS 528 allegedly sank a
lighter that was being towed by three tugs; in reality, not a single Soviet watercraft was lost on Lake Ladoga that day, although according to Soviet sources, the Soviet gunboat reported a fruitless engagement with two enemy motorboats). On September 1, 1942,
MAS 529 met two Soviet gunboats while on patrol off ; she engaged them by gunfire, before retiring unharmed (according to some sources, one Soviet naval boat was damaged, and a starboard engine of
MAS 529 failed; according to Soviet sources, the MO-class patrol boats , and participated in this action on the Soviet side; as a result of the engagement, six crew members of the Soviet patrol boats were wounded). On September 29, 1942,
MAS 528 and
MAS 529, commanded by Bianchini, encountered a Soviet convoy of a tug and barge train, escorted by a gunboat. They were able to manoeuvre into position to make a torpedo attack, but scored no hits. During October the force was involved in providing support to the land forces, as winter approached, and on 30 October the lake became too frozen for operations to continue. The XII MAS was evacuated from the base at Sortanlahti, withdrawing to winter quarters in
Tallinn. The spring of 1943 saw a change in the war situation; the decided to transfer the XII MAS to the
Mediterranean, though the four MAS boats were handed over to the
Finnish Navy rather than being transported back to Italy. == Aftermath ==