Opera 3 covered the anti-tank ditch that protected the Passo Tre Croci east of Cortina d'Ampezzo. Here you can see three embrasures of Opera 3. The left one was armed with a 47 mm gun, the two others had a light machine-gun. The opening between the two right embrasure is for the photophone. This sytem allowed the crew to communicate with a nearby work (In this case Opera 2) with light signals.