The Armalite MH-12 Maghook is a piece of equipment like a grappling hook, employed by the U.S. Marine Corps. Shane Schofield has used them many times, often saving his life.
"You know, one day your Maghook isn't going to work." - Book II on Schofield's luck with a Maghook
It is shaped like a Tommy Gun with a double handed grip. The 'head' of the Maghook is a magnetic plate, which can be switched on and off. There are also standard hooks that emerge from the plate so that it will act as a standard grappling hook. It has up to 150 feet of cable.
The MH-12A variant is smaller, about the size of a large pistol.
Some Maghooks were kept inside Marine One during the President's visit to Area 7. When the base's forces turned against them, Schofield and his team got a hold of a few of the Maghook's.
Astro offered Jack West Jr. his MH-12A variant when the team was trying to get back onto the Halicarnassus. Later Jack used it to reach the Vertex to keep Switchblade from dropping the pillar.
While falling into the chasm, Jack took Switchblade's Maghook from his back holster and used its grappling hook to stop his fall.
Schofield had a Maghook on him when his research unit was forced to confront a hostile force at Dragon Island, but upon seeing the French varient, the Magneteux, he opted to use them due to their better efficiency.