The Subspace Bomb (亜空間爆弾, Akūkanbakudan) is the primary weapon of the Subspace Army. When detonated, it removes the surrounding area from the world and deposits it into Subspace, leaving a dark void behind. The effect is additive; a larger area can be affected by causing multiple bombs to go off at once. Each bomb requires two Robotic Operating Buddies to function. The bomb keeps hold of the R.O.B.s' arms, so two R.O.B.s have to be sacrificed for each bomb. Why exactly the bombs were designed to act this way is unknown, although it is possible that they require power from the R.O.B.s to function.
Subspace Bombs were designed and built on the Isle of the Ancients. As such, there is a large factory on the island, able to store dozens of bombs at once.
The average Subspace Bomb has a detonation timer of three minutes. Presumably, this allows Smashers & Subspace Army members to leave the scene before the explosion. Since Subspace Bombs have always succeeded in exploding (unless they are damaged before activation), it is unclear whether the countdown can be stopped. The Smashers, or fighters of the World of Trophies, repeatedly attempt to stop the bombs from detonating but fail each time.
Galleom has a self-sufficient Subspace Bomb embedded in its head. This bomb does not require R.O.B.s (presumably drawing power from Galleom instead) and had a detonation timer of fifteen seconds. Since Galleom likely tried to blow up the bomb as soon as possible, it can be assumed it needed fifteen seconds to charge. Galleom used this bomb once it was defeated twice in quick succession, attempting to take revenge on Lucas and Pokémon Trainer as it blasted into the sky. The two managed to escape, and the bomb dealt minimal damage to the surrounding area, drawing Wario's trophy into subspace instead.
Subspace Bombs were surpassed in functionality near the end of the Subspace Emissary by the Subspace Gunship. The Gunship's primary weapon has the same effect as a Subspace Bomb, but can be launched from a great distance and can be used repeatedly without the assistance of R.O.B.s. Once the Gunship was complete, all remaining Subspace Bombs were detonated to open up a large enough hole in space for the Gunship to be deployed.