The Grapnel Gun allows Batman and his associates to scale up or rapple down tall buildings, or swing between Gotham skyscrapers on successive lines. Essentially, the gun contains a magazine of explosively-propelled darts attached to de-cel jumpline reels. Once fired the lines are secured with braking and clipping mechanisms inside the graphel gun sleeve.
Each grapnel "dart" possesses small drilling motors that activate upon firing with a micro-diamond drill head to enable attachment to light aluminum, steel or concrete masonry. The dart itself is also built to have various cables attached to it, such as snap-on mini-carabiner or high-test de-cel lines.
Grapnel guns can also fire an alternate "claw" attachement which, upon firing, latches onto or into an object and locks closed, securely "gripping" the object.
The Grapnel Gun was first introduced to Batman's arsenal following the release of the movie Batman (1989), where a small Spear-gun Grapnel was used. Before that Batman and Robin wielded a batarang and rope combination to navigate the Gotham rooftops.