Opel Blitz was a series of German Trucks. Blitz 3.6 three-ton version was used in large numbers. In real life only the Mechanized forces were able to have the motorized logistical support while the Infantry units had to depend on horse to carry their supplies.
The Blitz Mun. is a standard munitions vehicle. Use it to resupply units (especially artillery) and repair damaged tanks. If needed, units can be embarked (by right clicking them onto the truck), which can be used to quickly reposition artillery pieces, infantry units, or AT guns.