Editing Leo Marks (section)

===Gestapo activities and "Indecipherables"===
[[Gestapo]] signal tracers endangered clandestine radio operators, and their life expectancy in occupied France averaged about six weeks.<ref>{{Cite book |last=Marks |first=Leo |url=https://www.worldcat.org/oclc/40776827 |title=Between Silk and Cyanide : A Codemaker's War, 1941-1945 |date=1998 |publisher=Free Press |isbn=978-0-684-86422-8 |location=New York |page=602 |oclc=40776827}}</ref> Therefore, short and less frequent transmissions from the codemaster were of value. The pressure could cause agents to make mistakes encoding messages, and the practice was for the home station to tell them to recode it (usually a safe activity) and retransmit it (dangerous, and increasingly so the longer it took). In response to this problem, Marks established, staffed and trained a group based at [[Grendon Underwood]], Buckinghamshire to [[cryptanalysis|cryptanalyse]] garbled messages ("indecipherables") so they could be dealt with in England without forcing the agent to risk retransmitting from the field. Other innovations of his simplified encoding in the field, which reduced errors and made shorter messages possible, both of which reduced transmission time.