Released late in 1995 for the PC, Worms: Reinforcements (or Worms+, as it is often called) is an expansion pack for Worms distributed by developer Team17 and publisher Ocean Software. It was later bundled together with the original game and rereleased in 1996 under the name Worms and Reinforcements: United (i.e., Worms United). Perhaps the most noticeable new content in Reinforcements is a twenty-five-mission single-player challenge mode, which offers a series of battles, presented in a linear sequence, against A.I. opponents that grow in strength and difficulty over time. Progress through the challenge mode is not saved, however a password system is implemented that allows players to jump automatically to any level they have previously reached; a similar single-player structure would be adopted in 1997's Worms 2.
Other than the challenge mode, Reinforcements includes a number of more subtle gameplay alterations. The ability to switch between available worms at the start of a turn is added, as well as a new class of crates that restore hit points when picked up. The properties of existing weapons have been modified in some cases; Dynamite, for instance, has the ability to be thrown rather than simply being dropped as in the original. Additional audio and new custom levels are included as part of the package, as are new options for players to import levels and sounds of their own. Worms: Reinforcements also boasts IPX network and modem support.
Only one new weapon is introduced in Reinforcements: the Mole Bomb. Unfortunately, due to a bug in the release version of the game it is nearly impossible to find Mole Bombs in weapon crates, as they are intended to be found, and as a result most players will be hard-pressed to actually find, let alone use, the new weapon. In response to this issue, Team17 released details on how to alter "worms.cfg" in order to force the game to place Mole Bombs in the player's inventory by default. The coding error responsible for the Mole Bomb glitch was fixed in Worms United, though the aforementioned method can still be used to add extra Mole Bombs if the player so chooses.