Sins of a Solar Empire: Entrenchment is the first expansion pack of the Sins of a Solar Empire game. It was first released on February 25, 2009. In order to run the expansion pack, the original Sins of a Solar Empire game must also be installed. Entrenchment was developed mainly to add more defensive options for the original game.
Sins of a Solar Empire: Entrenchment features Defense Research Trees. This is where the upgrades for defense platforms, hangars and the like can be found. It also has the Star Base and Tactical Structures upgrades. The expansion pack also features Star Bases. These Star Bases are constructed using the Star Base Construction Cruiser, which can be researched on the Defense Research Tree. The Star Base enables players to strengthen gravity wells or colonize gravity well. Each player is entitled to construct one Star Base only. This expansion pack also enables players to build Anti-Structure Cruisers. These are ships that contain mammoth weapons. Mines are also made available to all races in, wherein a maximum of 150 can be deployed for every Gravity Well.
Aside from these new features, Sins of a Solar Empire: Entrenchment also made some changes. The defense platforms have now more upgrades. The Hangar Research is now available in the Defense Research Tree instead in the Combat Research Trees. Other changes include AI enhancements and new planet bonuses.