Arturo Barea, Struggle for the Spanish Soul.

Many paperback titles from publishing firms such as Penguin, Albatross, and Searchlight Books had thin paper jackets wrapped around their thin paper covers. The jackets provided additional space for publishers to use for blurbs, biographical (in some cases a photograph) notes on the author, and as with this particular title, promotion and listing of other Searchlight titles. This jacket was designed by the mysterious Zec.