On 20 August 1971, the battalion encased its colors in the Republic of Vietnam and moved to Fort Campbell, Kentucky, where it took the place of the recently deactivated 51st Engineer Battalion. Here the histories of the 20th and the 51st are combined. The 51st throughout 1971 had been conducted normal training and construction operations at Fort Campbell. The colors of the 20th were still in Vietnam for much of the year. When the colors of the 20th returned to Fort Campbell, the annual histories of the companies reflect the histories of the 51st Engineer Battalion as well as those of the companies of the 20th Engineer Battalion.
For the remainder of the 1971, the companies of the 20th conducted various post projects, NBCAIC (Nuclear, Biological, Chemical Accident/Incident Control) alerts, building improvements, 24=hour alerts, and short field training exercises. Each of the companies reported severe manpower shortages in their October histories. In a relief attempt, soldiers from the 173rd Airborne Brigade who refused jump status were reassigned to the 20th. Though this was a temporary fix in numbers, these soldiers were not up to the Engineer standard and many were AWOL within just a few months.
In 1971 and 1972, the Battalion was again completing construction projects on Fort Campbell including ranges, heliports, ammunition supply points, tank trails, and stockade building rehabilitation. Company D also worked on a civic action project in the Bowling Green, Kentucky community. The company constructed a recreation park, cleared debris, constructed a foot bridge, installed culverts and constructed picnic tables. HHC also provided construction expertise to the Hopkinsville, Kentucky Senior Citizen's Center by constructing a wood-working shop, roof renovations, and wiring and hanging florescent lights.
In 1972, the Battalion also participated in Operation Flamingo at Homestead Air Force Base, Florida. The operation involved loading 88 aircraft with soldiers, vehicles, and equipment as a deployment readiness exercise. The Battalion was still critically short soldiers and reported only a 35% fill of mechanics in October 1972. That same month the 114th Engineer Detachment (Fire Truck) and the 26th Engineer Detachment (Water Purification) were attached to the 20th Engineer Battalion. Construction projects in Flatwoods, Tennessee, Clarksville, Tennessee, and Eddyville, Kentucky were also completed as part of the Civic Action Program.
On 29 May 1973, the 20th Engineer Battalion was the first non-divisional unit at Fort Campbell to receive the coveted Commanding General's Outstanding Unit Award.
The Battalion also completed the Indian Mound Airfield for Fort Campbell in 1973. Company B and elements of the 326th Engineer Battalion reshaped and recrowned the runway and conducted rock crushing operations in preparation for Operation Brave Shield VII. The project also supported Operation Orbiting Eagle II in mid-November 1973.
Civic Action Projects were at the forefront of 20th Engineer Battalion missions throughout 1973 and 1974. The following projects were completed:
West Point, GA demolition of 1000 foot long, 85 foot high Seaboard Coastline Railroad Bridge spanning the Chatahoochee River
Cleveland, TN country recreation area including athletic fields and picnic areas
Clarksville, TN Fairgrounds Park
--End of Chapter 6, Fort Campbell