Walter Kempowski, a German writer and archivist who compiled thousands of pages of recollections from eyewitnesses of World War II into a monumental firsthand record of the German wartime experience, died at a hospital in northwestern Germany on Oct. 5. He was 78.

The cause was intestinal cancer, said his publisher, Albrecht Knaus Verlag.

Even in his final days, Mr. Kempowski kept a diary. His passion, for his own memories and those of others, led to the creation of the World War II work “Das Echolot: Ein Kollektives Tagebuch” (“The Sonar: A Collective Diary”), published from 1993 to 2005....

In the 1980s Mr. Kempowski ran a series of advertisements in German newspapers inviting people to send him documents, letters, diaries, reports or other recollections of their World War II experiences. His appeal drew an enormous response. He received mail from the prominent and the ordinary: doctors, soldiers and even high-ranking politicians.

The resulting book series, “Das Echolot,” was viewed as a literary and historical triumph. A German government spokesman, Thomas Steg, described Mr. Kempowski as “one of the most prominent authors in the German language.” His legacy has been widely discussed at the Frankfurt Book Fair, the world’s largest booksellers’ convention, which is running this week.