Sleeve gun

A sleeve gun is a device wrapped around a user's forearm and used to conceal a small firearm under a long-sleeved coat or jacket. A triggering mechanism causes the firearm to extend out of the gadget quickly enough for the user to grab it and fire.

The term "sleeve gun" was also used for an experimental device developed for the British Army during World War II by Station IX of the Special Operations Executive, essentially a noise-suppressed Welrod pistol minus the pistol grip.