Based on the HK69A1 grenade launcher, the grenade launcher in The Lost and Damned lobes 40 mm explosive rounds that detonate on a seven second fuse and inflict the same amount of damage as pipe bombs, making it ideal for removing cover, such as a large group of enemies or a pursuing car. The launcher also offers the advantage of being able to fire rounds over greater distances than those that thrown hand grenades can reach. Although the grenade launcher is not intended for aerial targets and is only a single-shot weapon (allowing the player to fire only one round before reloading), the player can carry more grenade launcher rounds than the Rocket Launcher allows (20 grenades compared to 8 rockets).
While the grenade launcher shoots rounds further and in a higher speed, rounds shot in long range are flung in an arc due to gravity and are not guaranteed to land in a particular spot, requiring the player adjust their targeting to take these factors into account (i.e. aiming higher than the target for long range fire), or rely on trail and error and inevitably waste ammunition. Experienced players can also fire the launcher in an angle where the round will bounce off walls to reach tricky targets.
In the Ballad of Gay Tony, grenades fired from a grenade launcher explode on impact if the round hits a vehicle or person. Also, the time it takes for the grenade to explode has been shortened to about four seconds.
In both The Lost and Damned and The Ballad of Gay Tony, the grenade launcher is available from gun vans (either via Terry Thorpe in TLAD or Armando Torres in TBOGT). In TLAD, the weapon spawns at the Lost MC Clubhouse and Brian Jeremy's Safehouse after completing 50 Gang Wars.
- The grenade launcher was to be included a weapon in Grand Theft Auto: Vice City and in Grand Theft Auto San Andreas, but was cut during development.
- In the PlayStation 2 version of GTA Vice City, its grenade launcher model (grenlanc.dff) and its textures (grenlanc.txd) can still be found in game files. These files were removed from all other ports of the game.
- The Grenade Launcher in The Lost and Damned may be a reference to the number 69 since the weapon is based on the HK69A1.