The development of three devices at the Naval Ordnance Laboratory required encapsulation of electronic assemblies for protection against shock and temperature-humidity effects. Partly, at least, due to the fact that these assemblies were somewhat larger than many encapsulated units, the original potting material cracked or caused destruction of the embedded components when subjected to the JAN Temperature-Humidity Test. The 28 day duration of this test and the necessity for providing a satisfactory material in a short time led to a program of simultaneous evaluation of a number of materials which appeared promising in generally similar applications at NOL and elsewhere. Each material was checked for its ability to withstand shock, vibration and temperature-humidity tests. Insulation resistance was measured both before and after temperature-humidity testing. The program eventually encompassed 27 material combinations, two of which proved to have exceptionally good properties for the application at hand. Additional experimentation was necessary to determine methods of applying pre-potting protective coatings to certain components, and to select components which would provide suitable reggedness and stability. The case history of the program depicts the all-out effort which often must be expended in solving problems of this type in connection with accelerated development projects, and points out the need for long range accumulation of practical data on encapsulation to facilitate their solution.