Dan DeBlanc was born on September 13, 1944, in Slidell, Louisiana. He joined the Marine Corps Reserve on November 5, 1966, and entered Officer Candidate School at MCS Quantico, Virginia, on March 20, 1967. DeBlanc was commissioned a 2d Lt in the U.S. Marine Corps on June 2, 1967, and completed flight training in August 1968. He was assigned to Marine Light Attack Helicopter Squadron 267 of Marine Aircraft Group 56 at Camp Pendleton, California, from September 1968 to January 1969, and then deployed to Southeast Asia, where he served with Marine Observation Squadron Two (VMO-2) of the 1st Marine Air Wing in the Republic of Vietnam from January 1969 to January 1970. DeBlanc next served with VMO-1, HMM-365, and HMA-269 of Marine Air Group 26 at MCAS New River, North Carolina, from February 1970 to November 1971. He then left active duty and served with HMM-767 at NAS New Orleans, Louisiana, in the U.S. Marine Corps Reserve from November 1971 to June 15, 1977.

His Silver Star Citation reads:

For conspicuous gallantry and intrepidity in action while serving as a Pilot with Marine Observation Squadron Two, Marine Aircraft Group Sixteen, First Marine Aircraft Wing in connection with combat operations against the enemy in the Republic of Vietnam. On 17 March 1969, First Lieutenant DeBlanc launched as Copilot aboard an armed UH-1E helicopter assigned the mission of supporting a Marine company which was heavily engaged in combat with a large North Vietnamese Army force near An Hoa in Quang Nam Province. Arriving over the designated location, he was informed by the Tactical Air Controller (Airborne) that the unit on the ground had sustained several casualties and was pinned down in an open rice paddy by a heavy volume of automatic weapons fire from enemy soldiers occupying well-concealed, fortified positions, and that, because of the proximity of the casualties to the hostile emplacements, supporting artillery fire and fixed-wing bombing could not be used. Undaunted by the deteriorating weather conditions and the heavy volume of enemy automatic weapons fire directed at his aircraft, First Lieutenant DeBlanc alertly located the hostile positions and ably assisted his pilot at the controls as they engaged the enemy. Throughout the ensuing four-hour period, he skillfully monitored his instruments and provided his pilot with a continuous flow of vital information which enabled his gunship to be maneuvered on repeated rocket and strafing runs and to deliver its ordnance on the North Vietnamese Army targets with pinpoint accuracy. Despite his vigorous efforts, the fortified positions of the vast enemy force provided adequate protection for the hostile soldiers to enable them to prevent the Marines from recovering their casualties from exposed locations. The pilot of the UH-1E, determined to provide maximum assistance for the beleaguered unit, elected to land his helicopter to evacuate the wounded men. During the landing and while the aircraft waited on the ground for the crewmen to embark a casualty, the helicopter became a vulnerable target for intensified enemy automatic weapons fire. Utilizing his rifle, First Lieutenant DeBlanc, fearlessly delivered continuous fire at nearby enemy gun emplacements, then ably assisted the pilot to achieve full power as they lifted from the hazardous area and delivered one casualty to the An Hoa Combat Base for treatment. On three additional occasions, the pilot landed to evacuate critically wounded Marines and, each time, First Lieutenant DeBlanc completely disregarded his own safety and boldly maintained a dangerously exposed position to provide covering fire for the crew and casualties, despite the enemy rounds impacting around him, some of which caused extensive damage to the helicopter. His heroic and selfless actions inspired all who observed him and were instrumental in saving the lives of four fellow Marines. By his courage, bold initiative, and unwavering devotion to duty in the face of grave personal danger, First Lieutenant DeBlanc inspired all who observed him and upheld the highest traditions of the Marine Corps and of the United States Naval Service.