Group of wounded officers recuperating at a military hospital, along with a Home Guard Colonel, decide to return to active service by sailing to France and blowing up Big Herman, a German gun that has been terrorizing the English countryside and preventing locals from using the outhouse.
Amusing take on The Guns of Navarone (released the same year) is not quite a great comedy, but affable enough. Milligan isn't given enough to do (indeed, his bits of schtick could be excised with no impact on the plot), but the cast is game, and Ron Goodwin's martial/farcical score is a highlight. Le Mesurier particualrly seems to be rehearsing for his future role in Dad's Army. And quite good special effects for a comedy!
Note: Credited cast listed first, with uncredited and unknown roles listed in order of appearance. Thanks to Gerald Lovell for helping ID some of the unknowns, too!