Complex sentence: Some historians have thus far sought to dismiss civil defense advice as mere propaganda, despite detailed scientific research programs laying behind the much-mocked UK government civil defense pamphlets of the 1950s and 1960s, including the prompt advice of ducking and covering.
Split into simpler sentences: Some historians have thus far sought to dismiss civil defense advice as mere propaganda. Despite detailed scientific research programs laying behind the much-mocked UK government civil defense pamphlets of the 1950s and 1960s, including the prompt advice of ducking and covering.