The essential features of equipment for mobile processing are outlined with reference to the development of small photographic laboratory vehicles for use in the Jield. The resulting air film processor, the Wainco Products Limited 392. is described and details are given of trials carried out to establish its performance for a range of tasks in both reconnaissance and survey. The tests cover the sensitometric and drying behaviour of several air films in current use and include an analysis of the dimensional stability o f j l m in the processor. Applications using direrent containers and eflectiveness in improvised situations are also described and possible future variants of the processor are suggested.