Question: Immerhof protected blockhouses that were constructed during a war that lasted how long?
Sentence (from "Ouvrage Immerhof"): In addition, Immerhof protected other Maginot works in the vicinity: the casemates of Kanfen, the infantry shelter of Stressling, the observation point and shelter of Hettange-Grande, and a number of nearby blockhouses constructed during the Phoney War.
Relevant evidence: Yes