Which of the following is NOT a type of propelled explosive device that may be impaled in a casualty?

The type of device that is not considered a propelled explosive device that may impact a casualty is the grenade launcher. While grenade launchers are indeed designed to launch grenades, they do so from a stationary or mounted position rather than projecting explosive projectiles in a manner that would result in direct impact injuries as seen with other types of devices.

In contrast, mortars are indirect fire weapons that launch explosive projectiles (mortar rounds) at a high angle, and these can certainly result in casualties when they detonate in close proximity. Rocket Propelled Grenades (RPGs) are designed to be launched from a shoulder-fired platform, and they explode upon impact, causing significant damage to targets. Similarly, 40mm projectiles, often fired from grenade launchers, are designed to be propelled toward a target and can cause injury upon impact.

Thus, the distinction lies in the propulsion and impact mechanism of each device, making the grenade launcher unique in this context for not being a propelled explosive device that directly impacts casualties in the same manner as the others listed.