From Worms Knowledge Base
This object is placed like a dynamite, but it is no weapon. Instead, the Fan has no ability other than to influence the direction and speed of the wind. The direction the Fan blows in is determined by the direction which the worm placing it is facing, and from that point on the Fan adjusts the wind strongly in its direction. It lasts a few turns before running out of power, and is destructable from the beginning. As an addition, the blades of the Fan are exposed and are harmful to any worm unlucky enough to come into contact with it while it is running.
Little more than a barrel, only without the big explosion. This object would simply add or subtract a value to the wind-gauge. Furthermore, multiple Fans would be more powerful, and opposing Fans would cancel out the effect of others.
This object would be particularly useful in fort games, if you want to protect your fort from bazooka shells. But perhaps a more beneficial use would be to influence the wind in preparation for an important para-jump, perhaps to invade an enemy area, grab a crucial crate or secure a tenable territory. Another use would be in preparation for using the Napalm or Mail Strike.
It may seem a bit odd that such a small object, even if hidden away down a tunnel, manages to influence the wind all around the landscape. Still, it's a unique weapon with unique uses.