At 13:20 hrs., the XI. AK receives word from AOK 6 that the invasion is on for the next day – code word is “Hindenburg 100535”. The message is delivered right into a meeting of the leading corps commanders discussing the outcome of an artillery exercise.
Between 13:59 hrs. and 14:41 hrs., the code word is given to all subordinate commands and divisions and XI. AK is requesting the assignment of Artillery Regiment 19 (AR 19) which is currently located as a training battery at the training grounds in Senne.
By 22:50 hrs., the commanding officers have moved into their HQ at Heinsberg and from AOK 6, code word “Danzig” is received, confirming the attack the next morning.
Source: KTB IV. AK (BArch. RH 20-11/13)