Exercise Northumberland was a major exercise set up to evaluate the performance of aerial and ground-based search assets, based on earlier work, in 1987, by the UK Home Office known as 'The O'Donnell Theory'.  It set out to update these historical findings based on current approaches and methodologies for searching on the ground and developments in aerial technology. 

Both Initial Response and Intermediate Phase search techniques were employed by both ground searchers and aerial assets including fixed and rotary wing piloted aircraft and fixed and rotary wing drones.  An evaluation of the performance of each search asset was made.

The challenges and logistics of setting up such an exercise will be discussed; the performance and effectiveness of each asset will be reported on and an outline of future research based on the outcomes of the exercise will be given.