An Engineering Drone shoulder mounted engineering suite that can be mounted on an SACU or an ACU. They are considered air units, but the "No air" pre-game restriction does not remove them from the game.
The drone automatically assists the unit it was build on, but it can be told to build structures seperately from the ACU. It will build these structures at the same rate as the ACU would.
They can also repair, reclaim, and capture, just like a typical engineer.
If you detach the drone from the ACU, it opens up a world of possibilites. You can tell it to build structure in a different part of the base, capture units, and repair existing ones. Since it can be used in no-air matches it can be used to place artillery and such on areas that are otherwise only accessible by putting engineers in air transports.