The phrase "three year long" is correct and can be used in written English.
You can use it when referring to something that lasted for three years, e.g. "The three year long project came to an end."
It looks like a settlement is looming in a near-three year long European Union antitrust investigation into Google's search practices.
Both student materials and teacher resources are available for all three year-long curricula.
The Department of Physics offers three year-long, entry-level physics sequences, the PHYSICS 20, 40, and 60 series.
The apparatus will be carried in space by means of a Russian satellite, due to launch in 2005, for a three year-long mission.
Infantry captains lead companies of about 120 soldiers, and most have served one, two or three year-long combat tours since 2001.
Based on documents from Football Leaks, French website Mediapart claims 19 Chelsea signings have been looked at in a three year-long investigation.
In 1907, Pablo Picasso encountered an African mask for the first time at the Palais du Trocadéro, which subsequently set off his three year-long African period.
Following the initial six-month intervention, participants were randomized to one of three year-long extended-care programs (face-to-face counseling, telephone counseling, or mail-only contact).
A three year-long longitudinal study with rural women enrolled in a primary care screening program in the United States reported a 37% re-abuse rate[ 10].
But that's not a market; the three-year long wrangle to secure the deal reflects that "five detainees" is not some going price for an American POW.
