Marine Corps is an add-on for the multiplayer warfare game Söldner: Secret Wars. Marine Corps' most prominent feature is the inclusion of combat on water. The expansion adds ships and vessels such as jet skis, patrol boats and amphibious vehicles. There are ten new maps in total with both island and desert scenarios. Various new weapons (including laser-steered rockets), vehicles, tanks (Leopard, Mungo...) and planes such as the Tornado and the Eurofighter are now available. Next to general improvements to the interface and COMM mode, certain weaknesses and strengths have been rebalanced.
Owners of the base game or the re-release Söldner: Secret Wars - Reloaded can still go into battle with players with the add-on, even if they don't own it themselves, if they apply patch 33588 that was provided prior to the release. All the new features of the expansion are then available, but the new weapons, vehicles and vessels are not accessible. However, if a player with the expansion drops a new weapon or leaves a new vehicle, it can be used by all players.
The game was co-developed by what was left of Wings Simulations, after JoWood had announced to close the studio, and a new development team: Project-Z development.