1. A system comprising:a tank configured to hold a dielectric liquid;
a rack, horizontally oriented and located within the tank and having a plurality of bays, each bay vertically oriented and configured to receive a corresponding device;
an air pump configured to drive an air flow;
two or more variable-buoyancy chambers mechanically coupled to at least one of the tank and the rack, each of the variable-buoyancy chambers comprising a fluidically-sealed plenum and wherein the at two or more variable-buoyancy chambers include a first variable-buoyancy chamber and a second variable-buoyancy chamber, wherein the first variable-buoyancy changer is configured to mechanically couple to a first mechanical coupling of a device-in-service and wherein the second variable-buoyancy chamber is configured to mechanically couple to a second mechanical coupling of a device-in-service; and
a control subsystem configured to control a buoyancy of the first and second variable-buoyancy chambers in order to cause the device-in-service to:
move vertically relative to the rack; and
to rotate relative to the rack between a vertical orientation and a horizontal orientation.