Two ciphers stacked. First every letter becomes a pair of letters taken from A, D, F, G and X, using a square. Then those letters are written into columns under a key word and read out in a new order.
Why those five letters? Because in morse they sound nothing like each other, so a tired operator with a crackling radio could not confuse them. A cipher designed around its own signal.
Broken by a man in a hurry
Germany introduced ADFGX weeks before its final offensive, and it looked unbreakable. A French lieutenant named Georges Painvin worked on it almost without sleep for weeks and lost fifteen kilos doing it. The message he finally read revealed where the attack would fall, and the French moved to meet it. Painvin never fully recovered his health.
Print this page and you get a worksheet: how the cipher works, where it came from, and the puzzles to crack, with the machine and the menus left off.
Print this page as a worksheet Its sheet in the pack Try the challengesLonger, harder and written for grown-ups. Worth a look when this page runs out.