James was born on the 12th of October 1878, in Alexandria, Virginia, and he attended the US Naval Academy after high school. After graduating with the class of 1902, he served the two required years of sea duty and was then commissioned as an Ensign. By the time he deployed to Mexico in 1914, James was a Lieutenant and it was his actions there that would earn him the Medal of Honor. The citation reads:

For extraordinary heroism in battle, engagement of Vera Cruz, 22 April 1914. Lt. Lannon assisted a wounded man under heavy fire, and after returning to his battalion, was himself desperately wounded.

James received the Medal of Honor on the 4th of December 1915, and he remained in the Navy though World War 2, earning the Navy Cross for his actions while commanding the USS Nashville in World War 1. He retired from the Navy in 1947 at the rank of Rear Admiral, after 45 years of service. Though I could not find any record of a wife, he did have one son, also named James, who died during World War 2 as a US Navy Ensign. James Patrick Lannon died on the 13th of March 1953, at the age of 74 and he is buried one row away from his son in Arlington National Cemetery: Section 8, Grave 6410-B.