How does StarCraft II unload a medical boat while it is moving?

When the medical boat is moving, press Unload All or press the shortcut key D, and then click the mouse on the medical boat, then it can be unloaded while moving.

the advantage of mobile unloading: when your crew is fully loaded, many boats will be unloaded at the same assembly point at the same time, which will be shot down by air defense because too many people can't unload quickly. Mobile unloading can solve this problem.