Banfield was the Austro-Hungarian Empire's highest scoring naval ace and the only airman to receive the the Knight's Cross of the Order of Maria Theresa. He was an excellent marksman, scoring all nine victories from flying boats. Flying in more than 400 sorties against the enemy, he was the first Austro-Hungarian airman to score a victory at night. Flying a Lohner two-seater on June 27, 1915, he scored his first victory, downing an Italian balloon near the mouth of the Isonzo River.

In February of 1916, he assumed command of the naval air station at Trieste until the war ended. Following his marriage to Countess Maria Tripcovich of Trieste in 1920, Banfield became head of his father-in-law's shipping company.