Werewolf Launchers are siege weapons which are only available to the Evil faction in Stronghold Legends. They cost 100 gold and their entire use rests in catapults Werewolves over enemy walls.
If you do not use Werewolves in your army, then you should not purchase any Werewolf Launchers as this unit will not benefit you.
Werewolves are strong and durable units however, and in masses can quickly overwhelm enemy defenders, including those armoured, and within seconds can take control of enemy gatehouses and other towers or important fortifications along an enemy wall or defence system.
Unlike other units such as Vampiric Creepers they cannot climb up walls directly themselves, therefore using Werewolf Launchers is a great shortcut to directly bringing Werewolves onto an enemy wall while allowing your other units to use the traditional Siege Towers or Laddermen to scale up walls.
While Werewolves can technically use this devices as well, it's a cleaner approach using Werewolf Launchers because you keep some of the number of troops down stationed trying to scale up enemy walls, often resulting in more troops then ladders.
You don't even necessarily need to catapult Werewolves onto an enemy wall. Werewolf Launchers can also catapult Werewolves beyond the enemy wall and into their castle, running around and causing havoc in their castle before turning and attacking any enemy defenders.
To do this, simply station your Werewolves nearby your Werewolf Launchers, select your Werewolf Launchers and get them to attack a section of enemy wall, a building behind it, or using the "attack a specific location" icon, attack a place on top of the wall (or the ground behind the wall) in order to start catapulting the Werewolves.
Note that the Werewolf Launchers may not be able to reach the top of the wall depending on where you place them, and may fire the Werewolves short. If this happens, they will be fired to the extremely vulnerable position of the bottom of the wall on the ground, despite attacking in the position you requested.
This is due to the short range of the Werewolf Launcher, and, unfortunately there is no way of detecting exactly how far the Werewolf Launcher will fire, this is purely a process of trial and error. If you are unsure whether you will be able to catapult Werewolves over the wall safely, it's best to practice with one or two Werewolves first to see whether this will work, before you start your main attack.
Once started, the Werewolf Launcher will quickly fire all nearby Werewolves over the wall in rapid succession, so if the lineup of the Werewolf Launcher is incorrect and you start your main attack, then you could quickly find yourself in a position where all or most of your Werewolves have failed to reach the wall if you have not tested this first.
Note that Werewolf Launchers cannot actually attack any unit in the game at all, and cannot defend themselves either. Their sole purpose is to catapult Werewolves over enemy walls and defences. This means that they are extremely vulnerable to ranged and melee units, and especially vulnerable to aerial units.
To minimise the risks, you may wish to use a Cat to protect your Werewolf Launchers against White Witch attacks and station Archers nearby in case of aerial assault by other units such as Dragons. Note that fire and freezing can affect the health of your Werewolf Launchers, although they cannot actually be frozen.
You will need 100 gold as well as 1 peasant from the campfire before you can recruit a Werewolf Launcher.