[1] It saw action in France and Germany, serving notably with the Army's T-Force intelligence assault force in the capture of German atomic weapons facilities and personnel as part of Operation Big.

[3] In April a core unit of 18-year-old ASTP volunteers and Army Air Corps trainees arrived for five months of combat engineer basic training.

[1] The battalion departed New York POE on 27 October and crossed the Atlantic unescorted aboard the converted luxury liner SS Mariposa, docking in Marseille, France, on 6 November 1944.

[4] Company A line platoons were located at Peira Cava, St. Martin Vesubie, and La Bollene—engaged in minefield work, demolitions, bridge building, road work, patrol activities and other combat engineer assignments, confronting the enemy-held forts Mille Fourches and La Forca, on the Alpine heights of l'Authion above the Turini forest.

Early in March 1945 Company A units were pulled back to duty on the Côte d'Azur, guarding key points on the shore between Nice and Menton.

In the weeks thereafter the battalion moved with the battle front, rushing forward with assault forces to secure vital intelligence targets with their records, equipment, and personnel intact.

[1] The 1269th was now functioning as the combat arm of the Alsos Mission, a military Intelligence assault force commanded by Colonel Boris Pash directed against the Nazi atomic weaponry program.

[1] On 22 April at Haigerloch, and for six days thereafter in the towns of Hechingen, Bisingen, Tailfingen, and Thanheim, the 1269th ECB participated in taking atomic scientists into custody, seizing laboratory records and equipment, and securing uranium, heavy water, and other items and materials important to the U.S./British Manhattan Project.

Leaving the Alsos Mission on 28 April, the battalion became one of the first combat units to enter Munich, advancing with Company C, 30th Regiment of the 3rd Infantry Division.

Company A spent three days, beginning 27 July, crossing the Neckar with a Treadway bridge and then dismantling it, to fulfill that Seventh Army assignment.

On 3 August, the 1269th ECB was relieved from attachment to the Seventh Army T-Force, under orders that the battalion be depleted and its personnel transferred to the 3rd Reinforcement Depot, near Marburg.

[1] Most of Company A troops were moved by train in 40 & 8 boxcars dating from the 1st World War from 14 through 16 August to Camp Tophat near Antwerp, by way of Kassel, Maastricht, and Liege.