Abstract: A military gas can vent cap is set forth wherein a step-adapter sleeve is threadedly insertable within an existing military gasoline-type can. An upwardly projecting portion of the adapter sleeve is of a diameter greater than the lower portion to provide a planar surface for interfittingly imposing pressure onto a resilient gasket positioned within an interior portion of an associated cap. The cap is provided in a first embodiment with a vent hole directed into a tubular vent portion positioned on an upper surface of the cap filled with porous brass stock material to enable venting of fumes from interiorly of the can and preventing water intrusion from the interior of the can. A second embodiment includes a porous brass positioning member securing the gasket to the interior surface of the cap to enhance movement of fumes therethrough and to the vent.