The Apollo and Shuttle spacecrafts used fuel cells for the production of electric energy and water. The hydrogen and oxygen for the fuel cells were stored as a supercritical fluid at a temperature close to the critical point to increase density without using very high pressure.
But how were those fuel cell tanks loaded on the launch pad? The temperature of gaseous high pressure oxygen and hydrogen was too high, the boiling temperature of those liquified gases was too low. The boiling point of O2 at 1bar is 90.188 K (−182.962 °C, −297.332 °F) and the Critical point is at 154.581 K, 5.043 MPa or 50.43 bar.
Did they fill the tanks with the proper amount of liquified gases, closed the valves and waited (may be using the tank heaters to speed up) for temperatures and pressures to raise to the wanted values for the supercritical fluids?