M79 grenade launcher, aka Thumper
The M79 is a 40mm grenade launcher used by the US Army. It was created to increase the firepower of infantry, giving them a more accurate weapon with better range than a rifle grenade, while remaining much less cumbersome than a mortar.
American soldiers nicknamed it, among other things, "Thumper" or "Blooper" because of the particular noise emitted when firing. Its main flaw was that, due to its size, the soldier carrying it often had only a pistol to defend himself with. This led to the replacement of the M79 by the M203, mountable under an assault rifle.