Ever since I learned about the infamous Vietnam War operation undertaken by the ARVN, I've been interested in its name -- precisely, what the meaning of "Lam Son" is, and what the 719 stands for/represents. I've done a quick search and Google but it's yielded no results -- or was the name of it completely jargon to confuse any potential leaks to North Vietnamese spies?
719 signified the year the operation took place in (1971), and the route the region it took place in surrounded (Route 9).
Le Loi, a national hero of Vietnam, was born in Lam Son, a small Vietnamese village. Le Loi was famous for ridding Vietnam of the Chinese, in the 1600s, and would hold particular significance for the forces as a result.
See here for further information on Lam Son and the significance of 719, and here for details about the name Lam Son itself.