[Guns America] Arms manufacturer Nammo is looking to increase the Marines’ flexibility when it comes to next-generation hand grenades. Currently, many branches of the military are open to suggestions on the subject of better hand grenades, and Nammo’s MK21 Mod0 solution is modular.The Marine Corps largely relies on the M67 Fragmentation Grenade, which is very effective as a "defensive grenade," but it can be too much when working in close quarters. Nammo’s modular grenade is an "offensive grenade" which relies more on concussion rather than fragmentation for effect.
The benefit of a concussion grenade’s limited reach is also its major drawback. To get around this limitation Nammo’s design can be stacked or daisy-chained into much larger, more powerful explosives.
By using one charge the grenade works like a concussion grenade with very light fragmentation. Two charges provide a more standard "defensive" grenade explosive, and three ‐ and even potentially more ‐ grenades can be linked together "to destroy structures," writes the Marine Corps Times.