The Roland J. Regan collection documents Regan's experiences during World War II largely through photographs and military memorabilia.

The photographs from 1943 show Regan in combat engineer training in Wales and England, including photos at the Lakenheath/Mildenhall Royal Air Force base. The photos from 1944 document Regan and his fellow combat engineers at the 348th Army Engineering combat battalion HQ in southern England, unloading supplies on Utah Beach during the week after D-Day, and in Paris in the fall of 1944. The photographs from 1945 show the close of the war in Germany, including Regan and fellow combat engineers building pontoon bridges across the Rhine, Elbe, and Sauer rivers, posing with German artillery, and meeting the Russian army, as well as the aftermath of the liberation of concentration camps. Many of Regan's photographs were published in the book From Boston to Berlin (2001) by his son Roland J. Regan, Jr. and Christopher Mauriello. The index in the collection lists the Dachua and Luekenswig concentration camps; the book From Boston to Berlin identifies some of the same images as taken at the Wobbelin concentration camp outside Ludwigslust.

The artifacts include both U.S. and German military memorabilia. The U.S. military memorabilia includes Regan's military emblems, ribbon bar, and dog tag. The German memorabilia includes a knife, pins, and belt buckles; all the German artifacts have a swastika or SS symbol.

Also included is a history of the 150th Engineer Combat Battalion produced by battalion staff immediately after the war.