M2 was the designation of a Rebel type B ion cannon minefield.
M2 was deployed by the Rebels at some point prior to the Battle of Hoth. It managed to ensnare Imperial Assassin-class corvettes Dagger 1 and Dagger 2 while they were hauling torpedoes and TIE Series starfighter parts.
A pair of Missile Boats were dispatched to free the corvettes and defend the repair operation carried out by Gamma-class ATR-6 assault transport Omega from the Rebel MC40a light cruiser Planka, which arrived to claim the prize the Rebel minefield had caught.
The Missile Boats destroyed the minefield, the Rebel cruiser, and the starfighters the cruiser launched. The Dagger group then entered hyperspace to continue their mission.