I found a damage chart at this page:
http://trainers.hitechcreations.com/81-tactics/bomber/1039-level-bombing-techniquesI think the values are still accurate.
Summary:
Each box of supplies takes ten minutes off the downtime of every object within a mile of the drop point.
Supplies must come from a different base. Field 10 can't resupply field 10, but it can supply any other field. Vehicle supplies do not have this restriction, they can come from anywhere.
Damage to a factory increases the downtime of the objects they supply. Damage to the radar factory increases the time the radar is down when it is destroyed.
Hangars and manned guns are down for 15 minutes, period. They are not affected by factory damage or resupply.
A vehicle can resupply or repair by picking up a box of vehicle supplies. The vehicle must be within 800 years of a supply box to pick it up.
I think that covers it. Hope this helps.