Schlechter Wolf

The Schlechter Wolf was a type of artillery shell produced in large quantities (PROSE: Unexploded WWII Bomb Warnings) which were deployed during the Blitz by the Nazi German Luftwaffe. (TV: The Doctor Dances) It was possible that the Schlechter Wolves were a sort of sleeper artillery. (PROSE: Unexploded WWII Bomb Warnings)

History
A Schlechter Wolf was set to destroy a Chula ambulance as a cover up for Jack Harkness conning the Ninth Doctor and Rose Tyler. However, in order to save their lives so they could help Nancy defeat the Empty Child plague, Jack used his stolen Chula warship to put the bomb in statis. It later detonated in space, destroying the ship shortly after Jack abandoned it to enter the Doctor's TARDIS. (TV: The Doctor Dances)

In mid-2005, after the Northern and Jubilee London Underground lines began to be refurbished, an exponential quantity of still-active Schlechter Wolfs were excavated in Bow, Pimlico, Kennington in London. Corporal Cameron Walker warned anybody attempting to salvage the shells to sell on ebay, due to the strong market for WWII artefacts, to leave the shells alone due to how lethal they were. The discovery of the shells and Corporal Walker's statements were documented in a press briefing filed by Corp Alex Balfour, embargoed until 08:00am on 28 July 2005. (PROSE: Unexploded WWII Bomb Warnings)

Behind the scenes
The appearance of the bomb entitled "Schlecter Wolf" is an instance of the Bad Wolf meme. Technically, the closer German translation for the term is "Böser Wolf", the name of the character in the Brothers Grimm fairy tale, "Little Red Riding Hood". "Schlechter Wolf" implies a wolf of inferior quality.