I used to live on the Western edge of the Bournemouth Control Zone in a rural gap between two built up areas. We often had military helicopters flying through this gap, especially at night around 2300 and at low level with no lights. I am currently reading the book The Workhorse of Helmand and discovered that Chinooks there operate in pairs and I believe that the ones flying low over my house was one of a pair with only one lit up. Of course this increased the noise level and the awesome effect of a Chinook coming right over your house with no lights was impressive. The change in noise level as they passed over head seemed to increase the dramatic effect. I have now downsized to a place just over a mile away so I still hear them but its not the same.