A subsea storage unit (15; 15'; 15"), comprising: - a pressure hull having a cargo hold configured for storing cargo (3, 7), and the pressure hull having a movable hatch providing access to the cargo hold; and - a base (2; 8) configured for supporting the storage unit on a seabed; - suspension means (11a,b, 35), whereby the storage unit, when in use, may be lifted and lowered in a body of water; wherein the pressure hull comprises a number of ballast compartments (24, 24'); characterized by: - the pressure hull comprising ballasting pumps; the ballasting pumps fluidly connected to inlet/outlet ports having valves, and the valves, when in use, are remotely controlled, and each ballast compartment comprises one or more ventilation valves, whereby air may be evacuated as seawater is flowing into the compartment, whereby the ballast compartments, when in use, are filled and emptied in a controlled manner through the inlet/outlet ports and using the ballasting pumps; and - on-board batteries, wherein the ballasting pumps are powered by the on-board batteries, and wherein the on-board batteries are positioned in a watertight casing in a dry environment within the subsea storage unit; whereby the subsea storage unit buoyancy is controllable by the plurality of ballast compartments and ballasting pumps. - a pressure hull having a cargo hold configured for storing cargo (3, 7), and the pressure hull having a movable hatch providing access to the cargo hold; and - a base (2; 8) configured for supporting the storage unit on a seabed; - suspension means (11a,b, 35), whereby the storage unit, when in use, may be lifted and lowered in a body of water; wherein the pressure hull comprises a number of ballast compartments (24, 24'); characterized by: - the pressure hull comprising ballasting pumps; the ballasting pumps fluidly connected to inlet/outlet ports having valves, and the valves, when in use, are remotely controlled, and each ballast compartment comprises one or more ventilation valves, whereby air may be evacuated as seawater is flowing into the compartment, whereby the ballast compartments, when in use, are filled and emptied in a controlled manner through the inlet/outlet ports and using the ballasting pumps; and - on-board batteries, wherein the ballasting pumps are powered by the on-board batteries, and wherein the on-board batteries are positioned in a watertight casing in a dry environment within the subsea storage unit; - the pressure hull comprising ballasting pumps; the ballasting pumps fluidly connected to inlet/outlet ports having valves, and the valves, when in use, are remotely controlled, and each ballast compartment comprises one or more ventilation valves, whereby air may be evacuated as seawater is flowing into the compartment, whereby the ballast compartments, when in use, are filled and emptied in a controlled manner through the inlet/outlet ports and using the ballasting pumps; and - on-board batteries, wherein the ballasting pumps are powered by the on-board batteries, and wherein the on-board batteries are positioned in a watertight casing in a dry environment within the subsea storage unit; whereby the subsea storage unit buoyancy is controllable by the plurality of ballast compartments and ballasting pumps.