Daniel was born on the 26th of July 1890, in San Francisco, California, where he also grew up and went to school. He went on to the US Naval Academy after high school and graduated in 1911, receiving his first assignment on board the USS California. The following year, Daniel was promoted to Ensign and he received a promotion to Lieutenant (junior grade) in May of 1915. Because he avoided getting drunk and consistently attended Catholic mass, many assumed he was a conscientious sailor: on the contrary. He had a devotion to duty and dedicated his time to naval gunnery, receiving the largest percentage of hits during a Pacific Fleet practice battle.

Daniel was married to Mary on the 23rd of July 1914, and their son, Daniel Jr, was born October the following year. At this point, Daniel was suspended from duty due to being blamed for ordering the wrong parts for a ship’s inability to continue its mission. He was to appear before a court-martial, but it was found that someone else had made this mistake and Daniel was acquitted and reinstated. However, at the age of 25, his hair had already turned grey, and it was noted that it was from the stress of the trial.

During World War 1, Daniel was on board the USS New Orleans, escorting cargo ships that were crossing the Atlantic Ocean. On one occasion, Daniel refused to give up on the rescue of a disabled British ocean liner and because of his persistence, and what was described as superhuman strength when securing a cable, the New Orleans was able to haul the ocean liner out of danger. After the war, Daniel, Mary, and Daniel Jr moved to Washington DC and he then was assigned to the USS Idaho in 1920 as a fire control officer for two and a half years. Following five more assignments and now the rank of Commander, Daniel was recommended to be the Naval Aide to President Roosevelt in July of 1938. This recommendation came from Roosevelt’s physician, Ross McIntire, who had met Daniel in 1917 while on board the USS New Orleans. Daniel filled this role for the next three years and was promoted to the rank of Captain.

Daniel was released from the role of Naval Aide to President Roosevelt in May of 1941, in order to take command of the USS San Francisco. In less than a year, he was promoted to Rear Admiral and appointed chief of staff to Vice Admiral Robert Ghormley, commander of the South Pacific Area and South Pacific Force. It was his actions while commanding US naval forces against Japanese warships, while on board the USS San Francisco, that would cost him his life and earn him the Medal of Honor. The citation reads:

For extraordinary heroism and conspicuous intrepidity above and beyond the call of duty during action against enemy Japanese forces off Savo Island on the night of 12 to 13 November 1942. Although outbalanced in strength and numbers by a desperate and determined enemy, Rear Adm. Callaghan, with ingenious tactical skill and superb coordination of the units under his command, led his forces into battle against tremendous odds, thereby contributing decisively to the rout of a powerful invasion fleet, and to the consequent frustration of a formidable Japanese offensive. While faithfully directing close-range operations in the face of furious bombardment by superior enemy firepower, he was killed on the bridge of his flagship. His courageous initiative, inspiring leadership, and judicious foresight in a crisis of grave responsibility were in keeping with the finest traditions of the U.S. Naval Service. He gallantly gave his life in the defense of his country.

Even though he had died, in addition to Rear Admiral Norman Scott, the battle had ended with a victory for the Allies. US Navy tactical techniques change soon after this battle after an analysis showed some flaws in Daniels decisions. On the 9th of December 1942, Daniel’s son, now a Lieutenant (junior Grade) in the Navy, received his father’s Medal of Honor from President Roosevelt in a ceremony at the White House. Daniel Judson Callaghan was 52 years old when he died on the 13th of November 1942, and he was buried at sea. There is a cenotaph for him at the Holy Cross Catholic Cemetery in Colma, California, as well as his name listed on the Tablets of the Missing at the Manila American Cemetery and Memorial in the Philippines.