black ops brigade

 A black ops brigade or black ops crew is a small group of volunteers, usually people who live in a district threatened by bushfire, who band together with whatever resources they have to supplement the work of the official firefighting brigade. Their resources are often a small water tank on the back of a ute and the usual equipment for mopping up spot fires.  While full of admiration for the official firefighters, they point out that they are more mobile than the larger firefighting appliances and can reach points that would not be accessible to the bigger units. 

 A black op or black operation is one carried out covertly by a government agency and not officially recognised.  While these firefighting black ops are not a secret, they are not part of the official organisational structure.