from a BBC survey about grammatical misuse http://news.bbc.co.uk/2/hi/uk_news/magazine/7595509.stm
10. Here's one they often get wrong on BBC news! BBC reporter: "Then they opened fire on us". This is incorrect. In military terms there are two methods of shooting at an enemy, controlled-fire and open-fire. I.E. you are not opening anything so using the past tense of open is incorrect. The correct expression should be "Then they open-fired on us"