"1939-1945, World War II: During World War II in Europe, bicycles were used behind the lines by both sides, especially by the Germans, and Finns. The Germans invaded Poland in 1939 using troops on bicycles being pulled by ropes attached to motor vehicles. Germans used them heavily in the conquest of Norway.
"Resistance teams used them in occupied countries much as the IRA did in Ireland. Canadian troops carried them along on D-Day. Paratroopers on both sides used them in large numbers. Japanese Paratroopers had a small-wheeled folding bike with high-rise handlebars."
Doesn't say exactly why, though.
Well, these photographs (sorry, no scanner on this computer) show the Canadians disembarking, carrying bicycles, UNDER FIRE. It makes sense that bicycles were used for messages and communiques, but it seems odd that bicycle-carrying Canadians would be in the forefront of the invasion; it just makes more sense that they would have followed, not led, the guys with the guns.