Upon graduation, he was commissioned as a second lieutenant through the Air Force Reserve Officer Training Corps (AFROTC) program at the university.

An advantage that the "Triple Nickel Squadron" pilots and WSOs had over other U.S. aircrews was that eight of their F-4D Phantoms had the top-secret APX-80 electronic set installed, known by its code-name "Combat Tree".

Combat Tree could read the IFF signals of the transponders built into the MiGs so that North Vietnamese GCI radar could discriminate its aircraft from that of the Americans.

Displayed on a scope in the WSO's cockpit, Combat Tree gave the Phantoms the ability to identify and locate MiGs when they were still beyond visual range (BVR).

Ritchie and DeBellevue's assignment on May 10, 1972, the first major day of air combat in Operation Linebacker, was as element leader (Oyster 03) of one of two flights of the F-4D MiGCap for the morning strike force.

At 09:42, forewarned 19 minutes earlier by the EC-121 "Disco" over Laos and then by "Red Crown", the U.S. Navy radar picket ship USS Chicago, Oyster flight engaged an equal number of MiG-21s head-on, scattering them.

Almost simultaneously Ritchie and DeBellevue rolled into a firing position behind the remaining MiG-21 of the original four with a radar lock, launched two AIM-7 Sparrow missiles and scored a kill with the second.

On July 8, 1972, Ritchie and DeBellevue were leading Paula flight in gun-equipped F-4Es instead of the Combat Tree F-4Ds they usually flew, on a MiGCAP to cover the exit of the strike force.

While they were west of Phu Tho and south of Yen Bai, the EC-121 vectored them to intercept MiG-21s returning to base after damaging one of the US chaff escorts.

The MiG turned to its right to evade the attack, an unusual maneuver and Ritchie used a vertical separation move to gain position on its rear quarter.

DeBellevue obtained a solid boresight (dogfighting) radar lock on it while at the MiG's 5 o'clock and although fired from the edge of their flight envelopes, both AIM-7s struck home.

The first MiG had also turned back and was attacking the last F-4 in Ritchie's flight from behind, an often fatal consequence to US aircraft employing the then-standard "fluid four" tactical formation.

Expecting the Sparrow to miss, he was trying to switch to a gun attack in the relatively unfamiliar F-4E he was flying that day when the missile exploded the MiG, 1 minute and 29 seconds after the first kill.

[6] Ritchie's final victory (his 5th making him an "ace") with DeBellevue (his 4th) came on August 28, 1972, while leading Buick flight, a MiGCAP for a strike north of Hanoi.

During the preceding month, 7th Air Force had instituted daily centralized mission debriefings of leaders and planners from all fighter wings called "Linebacker Conferences".

Red Crown, now the USS Long Beach, alerted the strike force to "Blue Bandits" (MiG-21s) 30 miles (48 km) southwest of Hanoi, along the route back to Thailand.

His skill as a weapon systems officer was recognized when he and the other two Air Force "Aces", Ritchie and Feinstein, received the 1972 Mackay Trophy.

His stated desire to train WSOs fell second to the Air Force determination that the highest ranking ace of the Vietnam War would not be a non-pilot.

Through his extraordinary heroism, superb airmanship and aggressiveness in the face of the enemy, Captain DeBellevue reflected the highest credit upon himself and the United States Air Force.