Operation Tiger was the dress rehearsal for D-Day. It cost many lives, but also saved many lives on D-Day.

http://www.kansasheritage.org/abilene/ikespeech.html

http://www.kansasheritage.org/abilene/ikespeech.html

https://www.history.com/news/d-days-deadly-dress-rehearsal

https://obamawhitehouse.archives.gov/the-press-office/2014/06/06/fact-sheet-normandy-landings

https://www.npr.org/2012/04/28/151590212/operation-tiger-d-days-disastrous-rehearsal

http://www.exercisetigermemorial.co.uk/story-exercise-tiger