Contra 4 is based on the same 2D gameplay system featured in the series through Contra III: The Alien Wars, ignoring many of the game mechanics introduced in later games such as the fixed weapon configurations in Contra: Shattered Soldier and Neo Contra, returning to the old method of picking up power-up icons to obtain new weapons. The play controls are similar to Contra III: The Alien Wars, including the ability to hold two weapons in inventory. (wikipedia.org).