In Stacy Schiff's Cleopatra we learn that Cleopatra was present on the battlefield at Actium, more precisely, on her flag ship at sea. I'm not sure if the boat actually went out and engaged with combatants but it is still quite an achievement. Something similar happened around 42BC during one of the battles which was an aftermath of Ceasar's assassination. This raises the question, how many female heads of state or at least very highly ranking have been on the battlefield. I can only think of Bodicea (not sure if she was queen) or Joan of Arc (definitely not a head of state). My mother mentioned Catherine the Great of Russia but I'm not sure if this is true.