In total 1,144 people wrote back, 172 of whom he interviewed. This great journalistic enterprise culminated in the publication of his book, The Longest Day, in 1959.
The book went on to sell 30 million copies in 30 different countries and few years later was turned into a Hollywood film (so too with another Ryan work, A Bridge Too Far).
But beyond the commercial success he provided a means by which veterans could talk about their experiences – often for the first time.
Later in life he received numerous letters from wives and mothers thanking him. Reading his books, they said, was the first time they truly understood what their loved ones had been through but could never bring themselves to openly talk about.
Ryan died young, of prostate cancer in 1974. Like any Fleet Street great his legends have muddied into truth over time.
So much so that in 2014 during the 70th anniversary of D-Day his biographer Dominic Phelan felt compelled to write into the Telegraph letter pages to correct a few of the taller tales.