My issue with the supply is the loss of supply convoys/transports between units that have absolutely no logic. Every time I lose a transport or x% I try to figure out why, but most of the time there is no reason for it whatsoever. There are no enemies between the sender and the receiver, they haven’t even moved in the last 4 hours, but they still manage to lose transports. My only consolation is to imagine that the enemy must be losing transports to thin air as well and hopefully they run out before me.
Pages 38 and 39 of the game manual explain a concept known as "line of sight." It deals in what a select unit can "see" at any point in the game.
Intel reports show what enemy units can be seen with the aggregate line of sight from all the friendly units on the board. It is guaranteed there are enemy units which can't be seen by friendly units.
Any of those unseen units could interdict a convoy either with their direct fire, or by calling in indirect fire so long as they have a line of sight to the route and sufficient weaponry and time to target and hit the site.
There was a serious effort several years ago to define supply routes by determining the type of route a supply convoy was most likely to choose among all available between the base and the unit it supports. They are largely a combination of the safest and the quickest route between the base and the supplied unit determined by the condition of a route which was previously used. In determining their safety, the game engine looks at the time of day, weaather conditions and the state of intervening terrain to pick routes which can't be seen or hit at least by direct fire.
In determining the quickest route, the convoy will be assigned (in order) to major highways, roads, railroad tracks, and paths before being asked to traverse open terrain between the supply base and the unit it supports.
The most immediate route being used in a pulse is selected from all available that hadn't been interdicted on a previous pulse.
Improved routes through woods and towns are the most problematic when selected because an enemy sited in them can't be seen except at a short distance and can inflict damage on a convoy from that unseen position.
If a commander wants to assure availability of safe routing of supply convoys, they should garrison at least the choke points along the most likely routes between a supplying base and the units which it supplies.
It provides three benefits:
1) It expands the aggregate friendly line of sight for detecting enemy units
2) "Safe" routes tend to use both terrain which avoids being seen or hit by fire and secondly routes through friendly unit areas of influence
3) Garrison units can be dispatched to chase away enemy units which locate in an area where they can interdict the most likely supply route