In contrast to the Medic, the Supply Convoy is faster and can be used for both offensive and defensive purposes. Put it in the middle of a friendly force, and they'll all receive a Movement bonus at the start of their turn, allowing them to push deeper into enemy territory. Once they get into the thick of the action, have the Supply Convoy hang back and move damaged units next to it so they can heal up and be ready to rejoin the battle sooner. Linking it to a light cavalry class unit with the Escort Mobility promotion is also a good idea, as the Supply Convoy will be able to move efficiently and safely at the same time, while also providing a constant speed boost to the cavalry unit.
Civilopedia entry Edit
With the advent of mechanized infantry, logistics grew increasingly complex. A motorized army can only travel as far as its fuel provides, which is why support convoys became the lifeblood of modern warfare. Motorized transports could bear food, fuel, and medical supplies with more reliability and efficiency than carts drawn by beasts of burden. They also allowed for faster relocation of mobile field hospitals or fuel depots when operating near a more fluid front.
Everything we know about Civilization 6: Rise and Fall - PC Gamer, November 28th 2017