A computer chassis construction for severe environmental conditions enclosing a plurality of circuit cards and a power supply includes a top cover, bottom cover, a pair of side plates and a pair of end plates secured together to form an airtight seal along all abutting edges. A backplane is fixed adjacent the bottom cover mounts a plurality of connectors for electrical connection with mating connectors along a first edge of each of a plurality of circuit cards. Mounting grooves for receiving second, third and fourth edges of each of the plurality of circuit cards are provided to rigidify the assembly. An internal partition separates the plurality of circuit cards from the power supply and the latter is also rigidly secured within the chassis. Integral cooling is provided for both the circuit cards and power supply.