Sleeve gun

Sleeve gun and wrist gun are generic terms for a small firearm designed to be concealed under a long-sleeved coat or jacket—in fictional examples there is often a device with a mechanism to extend it out into the hand to fire.

The "sleeve gun" was developed during World War II by Station IX of the Special Operations Executive.

[2][3] Between 150 and 200 of the guns were manufactured almost certainly by Birmingham Small Arms Company.

[4][5] A Mark 1 version was designed but it is unclear if it ever made it off the drawing board.

[6] Though designs vary, most fictional sleeve guns involve a small conventional pistol on a sliding or telescoping rail, which quickly releases the weapon into the hand for firing,[7] either by a trigger mechanism, or just the sudden movement of the forearm.