UK forces have been in Afghanistan since US-led forces launched Operation Enduring Freedom in 2001, targeting al-Qaeda and its Taliban supporters.
5. Weak in intellect; destitute of ordinary strength of mind; foolish; witless; simple; as, a silly woman. 6. Proceeding from want of understanding or common judgment; characterized by weakness or folly; unwise; absurd; stupid; as, silly conduct; a silly question.
The Online Etymology Dictionary speculates that the word is an alteration of the 1940s term nert (meaning stupid or crazy person), which is itself an alteration of  nut . The term was popularized in the 1970s by its heavy use in the sitcom Happy Days.