PlanetsCentral

After choosing the target (if applicable), the Cargo Transfer window displays the unit you started with on the left, and the target on the right.

• Up, Down: Choose kind of cargo to transfer
• Left, Right: Move 10 units. With prefix argument, move that many
• Shift‐Left, Shift‐Right: Move 1 unit
• Ctrl‐Left, Ctrl‐Right: Move 100 units
• Alt‐Left, Alt‐Right: Move as much as possible. With prefix, move as many to make the left/right unit have exactly that many.
• U: If one unit is a planet, move all T/D/M/$/Sup/Colonists to that unit
• S: If one unit is a planet, toggle automatic supply sale. Supplies you move off one unit appear as megacredits on the other

Reference

Keys:

C and U from control screens and visual scan