"I Shackle"
The phrase "I shackle" in the days of Vietnam met to encode numerical map coordinates, typically 6 digits at a time while transmitting over the radio.
Do you remember...
Radio Team Operator:."Mother 3 this is Conviction 63, request medivac, over"
Base operator:.........."Roger, Conviction 63 send, over"
Radio Team Operator:."This is Conviction 63, have 2 wounded by gunfire, head and torso, I shackle, bravo-zulu whisky-quebec romeo-xray hotel-lima oscar-lima kilo-
sierra unshackle, request ASAP please"
Base operator: ........."Roger, Conviction 63, I shackle 'bravo-zulu whisky-quebec romeo-xray hotel-lima oscar-lima kilo-sierra unshackle, over"
Radio Team Operator:."This is Conviction 63, that's affirm, how long? over."
Base operator:.........."Conviction 63, Mother 3, medivac airborne, is LZ secure? over."