Units consume their supplies, both in the course of existence, and by motion/combat. The rate depends on game and unit type; it consists of an overhead consumed each turn without fail, and consumption for each cell of movement. The total is a max, not a sum, since units with a constant consumption rate are not likely to need additional supplies to move (consider foot soldiers who eat as much sitting around as they do walking). Supplies may also be consumed for production and repair, again depending on game and unit types, but this consumption happens during the build phase. Consumption is not affected by the situation of the consuming unit; armies in troop transports eat just as much as when in the field.