Lieutenant Colonel Sean Flynn.

Lieutenant Colonel Sean Flynn, a veteran of Iraq and Afghanistan, will mark his last day in command of the First Battalion of the 69th Infantry, the legendary Fighting 69th, by blowing the ceremonial whistle which officially starts the 255th New York City St. Patrick’s Day parade March 17.

On Flynn’s signal at 11 a.m. sharp, the Fighting 69th will step off from 44th Street and Fifth Avenue, first in the line of march as it has been in every parade since 1853.

At the conclusion of the parade, Flynn will turn over command of the Fighting 69th, a post he has held for two years, to Lieutenant Colonel Don Makay.

The St. Patrick's Day Parade making its way up Fifth Avenue.

The St. Patrick's Day Parade making its way up Fifth Avenue.

“Signaling the start of the parade this anniversary year is a distinct honor for me as both an Irish American and the commander of the 69th Infantry. It reminds us of the obligation that free societies must pursue to preserve the basic human rights and dignity of all men and women,” said Flynn, who is from Delmar, New York.

More than 200,000 people are expected to follow the Fighting 69th up Fifth Avenue.

This year’s grand marshal is Senator George Mitchell, who negotiated the Good Friday Agreement in Northern Ireland. The parade commemorates the 100th anniversary of the Easter Rising.

All of the traditional Irish organizations, including 49 Ancient Order of Hibernians groups, have signed up to march.

Crowds taking in the sights on St. Patrick's Day.

Crowds taking in the sights on St. Patrick's Day.

There will be more than 300 marching groups, including 150 bands, featuring the New York Police Department Emerald Society Pipes and Drums and the Fire Department Emerald Society Pipes and Drums, as well as pipers from Galicia, Spain.

Units from Óglaigh na hÉireann, the Irish Defense Forces, and An Garda Síochána, Ireland’s National Police Service, also will march.

The parade will be broadcast live on WNBC-TV 4, Thursday, March 17, and live-streamed on nbcnewyork.com. For the first time ever, the parade will be broadcast live in Ireland and the United Kingdom by IRISH TV.

Flynn is the latest member of his Family to serve with the Fighting 69th in combat. Since the regiment was formed in 1851, one or more of Flynn’s ancestor’s has served with the Fighting 69th in each theater of war it has deployed.