You cant defeat your own army, however, this happened:
10:21 PM Autumn 1912, Diplomacy: Your fleet at Tuscany successfully supported the fleet at Tyrrhenian Sea move to Gulf of Lyons.
10:21 PM Autumn 1912, Diplomacy: Your fleet at Tyrrhenian Sea moving into Gulf of Lyons recieved move support from the fleet at Tuscany.
10:21 PM Autumn 1912, Diplomacy: Your fleet at Ionian Sea successfully supported the fleet at Naples move to Tyrrhenian Sea.
10:21 PM Autumn 1912, Diplomacy: Your fleet at Naples moving into Tyrrhenian Sea recieved move support from the fleet at Ionian Sea.
10:21 PM Autumn 1912, Diplomacy: Your fleet at Tyrrhenian Sea attempted to attack the fleet at Gulf of Lyons, but failed.
10:21 PM Autumn 1912, Diplomacy: Your fleet at Naples sucessfully defeated the fleet and moved into Tyrrhenian Sea.
10:21 PM Autumn 1912, Diplomacy: Your fleet at Tyrrhenian Sea was overwhelmed by an attack from the fleet from Naples, and forced to retreat.
Game ID:354