"The Mercedes-Benz Unimog was an all-purpose utility truck first released in 1947. The terms of surrender imposed on Germany included severe limitations on military manufacturing. As such, the Unimog was originally designed as a civilian agricultural vehicle. It became quite successful and was eventually adopted by the fledgling West German Army, then by other armed forces around the world. The Unimog is known for its ability to handle virtually terrain and has been used in a number of military capacities, including as a troop transport and a field ambulance. New models in the Unimog line are still being released".
Since Supply Convoy cannot attack and are defenseless, use Elite Infantry or Veteran SMG to defend them and cover them from enemies and defenses.
Supply Convoy only heal the closest damaged troop. If you want them to heal a troop that is badly damaged and distances away, try to recall by rally your troops to a safe spot so your Supply Convoy can heal it.