As the American 96th Infantry Division advanced south along Okinawa's Highway 1 on 4 April, it came under increasing fire from the south and from the ridges on their left (east). Three medium tanks from the 763d Tank Battalion were destroyed by a carefully sited and well-concealed 47 mm anti-tank gun. Firing twenty rounds, Japanese gunners set the three tanks afire. Japanese Army commanders later described this feat as an illustration of the effectiveness of 47 mm guns. "Great results," Japanese combat instructions stated, "can be obtained by concealing the guns and opening surprise fire on the tanks at close range."