Given that humans are getting taller as time passes, the likelihood is that the tallest soldier served relatively recently.

Here is an article on a German soldier who fought in WW2 who was 7'6": http://www.telegraph.co.uk/news/newstopics/howaboutthat/7813500/Tallest-German-surrenders-to-short-soldier-in-Second-World-War-picture.html.

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