Warship Gunner 2 is the sequel to the popular Naval Ops: Warship Gunner from Koei that debuted in 2003. Naval Ops: Commander, released in 2004, was based on the first game, but, because it featured a different type of gameplay featuring usable escorts, seems not to have inherited the status as the second game in the series, similar to how Koei's Samurai Warriors is based on the Dynasty Warriors gameplay. The sequel seeks to expound on the first title by revamping the visual engine, providing a new campaign and dozens of new features, and work on the bugs that held its predecessor back from being a truly great game. Featuring over 100 missions and all sorts of ships including submarines, battleships, destroyers, cruisers, and more, Warship Gunner 2 hopes to appeal to a large base of action-oriented fans.
The game is set in 1939 of an alternate universe, and thus combines technology of this period in the real world with a variety of futuristic lasers and weapons, without the "World War II-only" mode of the first game. However, the first playthrough is generally "World War II" consistent, while subsequent playthroughs feature more lasers and high-tech weapons en masse, as well as a slightly extended ending run. (After the first playthrough one can choose whether a mission played in Training will use its "1st playthrough" or "subsequent playthroughs" version, called Enemy Deployment 1 or 2.) Regardless, game balance and experience can be drastically affected by the Difficulty, the extent of the player's Parts inventory (whether picked up or R&D'd), the player's chosen ship for a mission, and how the ship was designed.
The story follows three or four officers of a Wilkia Freedom Forces naval crew Captain Schulz, Lieutenant Nagi, Commander Braun (German Federal Republic, attached to the crew), optionally with Commander Tsukuba (Japan) and Lieutenant Commander Werner (Wilkia), as they lead the resistance to the coup that overthrew their King on March 25, 1939, then declared an Empire led by Admiral Karl Weisenberger and started making war, in a manner akin to real-life Nazi Germany, albeit with the trump card of "superweapons," huge, heavily armed and armored vehicles at sea, in one case on land (a version of the Dora railway gun) and in two cases in the air. Over time, and particularly in the final mission of the second playthrough, the superweapons themselves take further prominence are more is learned about their nature, although their origins are left ambiguous. Wilika is portrayed as a colony of the Dutch that developed into a second "overseas homeland" with a separate ruling king and independent military. In effect the game consists of a group of Evil Dutchmen trying to conquer the world with advanced technology.
Although the same general story applies in all cases, there are three story paths with exclusive missions, "takes" on the story, and endings. The specific story path is chosen by the player's actions in the first two missions of the story and represented by your executive officer ("adjutant") being Werner, Tsukuba, or Braun (whose rescue and joining the FF is in all three story paths). After completing a first playthrough where Weisenberger goes down with a superweapon upon its sinking, all subsequent playthroughs have Weisenberger escaping to a superweapon submarine, then a final superweapon has to be fought in a mission whose introduction changes the general ending quite a bit.
In the game you can unlock the Zumwalt class Destroyer, as a Secret Blueprint (pre-configured ship design) which can be picked up (as a Parts crate) during the enemy deployment 1 boss battle; it does not however look like the conceptual designs of the real-life Zumwalt class, and it like destroyers and Secret Blueprint designs in general are inferior to many designs that are possible after sufficient research is done.
Source: Wikipedia, "Naval Ops: Warship Gunner 2", available under the CC-BY-SA License.