I believe it was Z-Axis Control, in the "Globals" group.
To use it, left click on the "move" button in the ship's abiltiy tab (or use the appropriate hotkey for it, was it D?) then move your mouse over the point you want the ship to reach in the 2D pane. After that, press the hotkey that you assigned to Z-axis and move your mouse up/down - the destination will go up/down accordingly.
It's the biggest cheat in the game ATM, by the way.