1. A cooling device for fluid submersion of electronics, comprising:a coolant container which encloses at least a portion of a coolant space;
a connection block which is mechanically attachable to the coolant container, the connection block having a coolant-space-facing surface and an environment-facing surface, the connection block having an internal electronics connector on the coolant-space-facing surface and having an external electronics connector on the environment-facing surface which is electrically connected to the internal electronics connector;
a coolant input located on the environment-facing surface, the coolant input having an inlet to the coolant space;
a coolant output located on the environment-facing surface, the coolant output having an outlet from the coolant space; and
a closure which is operable to seal a volume of a coolant and at least one electronics device in the coolant space inside the coolant container when at least a portion of the at least one electronics device is submerged in the coolant and when the at least one electronics device is mechanically and electrically connected to the internal electronics connectors;
wherein the coolant input and the coolant output each physically engage with a respective coolant connector in a rail, thereby providing respective coolant paths between the rail and the coolant space; and
wherein the external electronics connector physically engages with and electrically connects with at least one rail connector in the rail, thereby providing at least one of the following between the rail and the internal electronics connector: a power connection, or a data signal connection.