top tip ref the last post...
if your likely to be out in the rain trying to write orders, a permanent pen is useless... they dont write in the wet.
best bet is waterproof paper and a nice softish pencil (anything harder than HB will tear the paper)
next best is the waterproof nirex and a chinagraph
sorry to be a spotter but I have bitter experience of trying to write platoon orders for an ambush in Ballduff in the Highlands during a blizard last February.