The device, about the size of a person’s thumb, made a metallic clicking sound, and was an essential bit of kit for those landing in Normandy on June 6, 1944, under the cover of darkness.
Hollywood actor, John Wayne, helped the clicker become widely known from his dialogue in the 1962 film The Longest Day. “So: one click is to be answered by two clicks, and if you don’t get that answering click, hit the dirt, open fire.”
After parachuting into Sicily in 1943, Major Taylor, the future commander of the 101st American Airborne Division, realized the importance of communication within the parachuted units in enemy territory. Indeed, scattered in many places, isolated parachutists had difficulty in finding their comrades without risking exposure themselves to enemy fire.
Only the 101st Airborne Division was equipped with crickets, and only the paratroopers of the division received it a few days before June 6, 1944. In addition to this means of recognition, a voice code was developed (valid for 24 hours following the start of operations): “Flash”, was a word to which it was necessary to answer “Thunder”. On the second day, the code became “Hustle”- “Along”. Other means of identification existed: smoke (colored or not), panels, light or flags.
Clicker in CSS Museum