A door for mission critical enclosures, for example, cabinets containing sensitive items, such as electronics that may be exposed to high stress environments, for example shock and vibration. The door structure described provides improved mounting and lock features that can allow easy access while maintaining rigid structural needs and integrity. A door assembly for a cabinet generally includes a door that can be fitted directly, or indirectly, to an enclosure through an adapter frame. Generally, the door has fitting structures that operate as interlocking, tight fitting key sets. The fittings provide suitable detent features. An actuatable lock mechanism respectively locks and unlocks the door. The actuatable lock mechanism includes a ramped locking bolt that can engage a ramped surface of the cabinet or adapter frame to facilitate locking and unlocking of the door.