The Weapon Schematics are one of the most important bonus items in the game. It only occur as a primary or secondary target, to accomplish the respective mission. It is needed to get acces to newer and better Weapons.
You are revarded 500 points to your Score in the Mission Debriefing for picking up the weapon schematics, and the schematics will be used to process a new and more advanced kind of fireworks weapon. Allied and Axis sides has different unlockable weapons. They are usually well guarded, or you may also have to kill an enemy unit to get hold of it.