Q.B.I. was in operation at Croydon or Heston.

[pgarwood]

I am researching the early days of WWII. In 1939 the London Balloon Barrage was instructed not to fly if-"Q.B.I. was in operation at Croydon or Heston." Can anyone help my tired brain with the acronym Q.B.I.?? Thanks

 

[fubar57]

There is a list of three letter "Q" codes here... Q code - Wikipedia
Possibly this

 

[pgarwood]

There is a list of three letter "Q" codes here... Q code - Wikipedia
Possibly this

View attachment 821341

Thanks a lot fubar57 Good old Wiki!