'Boojum' is a term coined by Lewis Carroll, and first appears in his poem, "The Hunting of the Snark". The 'Snark' (SM-62) was a surface-to-surface missile (a large cruise missile) used by the US military. Given the presence of a missile base in the film, it is likely that the term, 'Boojum', was used to make the connection with the real missile.