Defending Rohan during the battle of the Pennor Fields

[Belegorn]

There may be spies who are made use of. I'm not sure how much they are used in M-E but I'd think they would definitely be made use of since it's really just a guessing game in war or battle otherwise. Spies are a must. I'd think the Elves would be best at it especially so since they could actually use their abilities to really blend into the enemy. Although they could be found out as Sauron did when he was being careful of spies with Felagund. There might be converted spies within the enemy camp as well that they could send messages through.