Commanding the 137th New York Volunteer Infantry, he played a key defensive role on Culp's Hill in the Battle of Gettysburg.

Listed in the 1860 census as "Clerk in Express", living at Washington and Gansevoort Street in lower Manhattan.

[1][self-published source] As lieutenant and adjutant of the 79th New York Volunteer Infantry, he fought with the regiment in W. T. Sherman's Third Brigade in the First Battle of Bull Run.

With James Cameron killed in action, and many of the unit's officers resigning, a number of the men mutinied.

On September 11, 1861, he led the regiment in an ambush of Confederate troops at Lewinsville, near Falls Church, Virginia.

[3] From Washington, Ireland and his regiment were sent directly to join McClellan's Army of the Potomac, in camp near Frederick, Maryland, after the Battle of Antietam.

[5] Led by Ireland, the regiment made several forays from its camp (at Bolivar Heights above Harpers Ferry) into northern Virginia in late 1862.

During the Battle of Gettysburg, Ireland's regiment was at the far right of the Union line, defending the trenches on Culp's Hill on July 2, 1863.

They withstood numerous attacks by the superior Confederate forces of Maj. Gen. Edward "Allegheny" Johnson, holding a vital position.

[14] Col. Ireland's fellow officers, meeting on September 10, expressed their regret for "his untimely death, as it were, "On the field of his fame and glory".