9/11 sent them to war. 25 years later, veterans grapple with what followed

John Byrnes was swimming in a pool beneath Hunter College in Manhattan on the morning of Sept.

11, 2001, when he stepped outside for coffee and heard sirens blaring down Lexington Avenue.

He learned that a plane had hit the World Trade Center .

Minutes later, he saw the North Tower collapse on a campus television and immediately headed toward his National Guard armory.

Byrnes spent the next two weeks helping secure Ground Zero.

And spent the following years in both Iraq and Afghanistan.

Each of the five veterans who spoke with Fox News Digital ahead of the 25th anniversary of 9/11 remembers where they were when they learned the nation had been attacked — and how Sept.

11 changed the trajectory of their life and service.

Some were already in uniform.

Others, including a successful businessman and a teenager who watched the attacks unfold on television at his school, felt compelled to enlist.

Looking back 25 years later, Byrnes draws a sharp distinction between the wars, including the decision to respond to the terrorist attacks and the choices that followed to continue the war on terror.

"The decision to go to Afghanistan , that was absolutely necessary," Byrnes, who is now a strategic director at Concerned Veterans for America, told Fox News Digital.

"The decision to go to Iraq, which was not necessary." "The decision to stay in Afghanistan for so long was unfortunate, but it all came down to that day." ARMY VET LAWMAKER MARKS ABBEY GATE ANNIVERSARY WITH BLISTERING MESSAGE FOR BIDEN-HARRIS: 'ABJECT FAILURE' "The decisions that didn’t seem wrong at the time were just pebble after pebble into an avalanche," he said.

Veterans who spoke to Fox News Digital all went to war believing they were protecting Americans by keeping the fight "over there." Twenty-five years later, they remain proud that they answered that call.