A computer and a chassis construction for a computer for severe environmental conditions enclosing a plurality of circuit cards and a power supply includes a sealed, airtight, watertight, metal enclosure having a plurality of integrally joined walls, a first of the plurality of walls having a removable plate for access to the printed circuit cards and the power supply accommodated in the enclosure. The computer for use in a severe environment includes a plurality of printed circuit boards and a power supply and a metal enclosure having a plurality of walls, a top cover and a bottom plate, the enclosure being integrally formed to form an airtight seal along abutting edges thereof. One of the walls has a removable plate and the enclosure is formed of metal. A mechanism is provided for preventing ingress of foreign substances in the enclosure. The mechanism includes a device for shielding the interior of the enclosure from electromagnetic interference (EMI). The computer preferably includes a personal computer-based architecture formed by the plurality of printed circuit boards and the power supply. The sealed enclosure is preferably adapted to meet Aeronautical Radio Incorporated (ARINC) 404 and 600 form factors. A thermal mechanism is provided for a direct thermal path from the printed circuit board components to a chassis sidewall. Such a thermal mechanism and resulting direct thermal path advantageously maximize the use of the sealed enclosure in severe environments.