UGM-84A heads for 10 Downing Street. (TV: World War Three)
Harpoon missiles were weapons invented by humans in the 21st century and were only used by armed forces.
In March 2006, Mickey Smith hacked into the UNIT website and released a harpoon missile designated UGM-84A under the Ninth Doctor's orders. This missile hit 10 Downing Street and completely destroyed it, and the Slitheen inside (with the exception of Blon, who teleported away), thwarting their plot to irradiate the Earth. The only thing left standing was a durable cupboard where the Doctor, Rose Tyler and Harriet Jones took cover when the missile hit. (TV: World War Three)