In the last war the Lancaster WOp/AGs used to set up the T1154/R1155 HF radios on the ground by sending 'Best Bent Wire'
dah di di dit, dit, di di dit, dah,
dah di di dit, dit, dah dit, dah,
di dah dah, di dit, di dah dit, dit.
[I've had to put commas in as this site won't let me double space]
I seem to recall Len Deighton mentions this in his book 'Bomber'