Jacks are additional national flags flown by warships (and certain other vessels) at the head of the ship. These are usually flown while not under way and when the ship is dressed on special occasions.
On the Naval Jack of Italy there are four quarters referring to the four Medieval Italian Thaloaasocracies or Maritime Republics (Repubbliche Marinare on Italian)
1st quarter: on red, the golden winged lion of S. Marco wielding a sword while is closed the book normally showing the phrase “Pax Tibi Marce evangelista meus” (Republic of Venice)
2nd quarter: on white field, the red cross of S. Giorgio (Republic of Genova)
3rd quarter: on blue field, the white cross from which came later the Malta cross (Republic of Amalfi)
4th quarter: on red field, the white cross with 12 balls reminding the Twelve Apostles (Republic of Pisa)
The jack shown above is flying on an Italian Submarine during a visit on board with a group of seamen: a special thanks to the Captain who kindly hosted us.