The Fluttos were good sea-boats with improved internal arrangements, hull strength, anti-aircraft armament and diving times.

Of these 10 were commissioned and saw action; two others were unfinished at the Italian armistice in September 1943 and work on them was abandoned.

The second series of 24 were to the same design, though enlarged slightly to resolve trim problems highlighted in the first vessels.

Most of these hulls fell into German hands, and work was continued on several, but none became operational before Germany's surrender in 1945.

The third series were a copy of the Type II design, and were due to be started in 1943, but none had been laid down by the time of Italy's surrender in September of that year.