pb?Paperback. Typically 7" by 4.25" (18 cm by 11 cm) or smaller, though trimming errors can cause them to sometimes be slightly (less than 1/4 extra inch) taller or wider/deeper.
Notes: Artist not credited.
According to www.penguinsciencefiction.org the cover shows ''The Control Room, Civil Defence Headquarters'' (1942) by William Roberts