The story of Steel Diver:
In the year 2011, a ‘power-hungry rogue nation’ invaded several nearby countries. A secret organization known as the ‘Steel Divers’ was formed from various countries' navies to combat this threat. The Steel Divers travel through various areas including Arctic and jungle settings and are eventually tasked with destroying the enemy stronghold. In the last mission of the original Steel Diver, the final boss of the game was the Giant Z-Class submarine. The front hull of this sub is placed with spikes, although this probably serves to intimidate enemies, because in-game it has no mechanical purpose. This sub also appears in the sequel Steel Diver: Sub Wars, as a submarine purchasable in the online shop.

Gameplay (Original Steel diver):
Steel Diver consists of 3 main modes: Missions, Periscope Strike, and Steel Commander. Missions is further broken down into 2 modes: Campaign and Time Trials. The main gameplay occurs during Campaign. In Campaign, the player uses sliders and dials on the touchscreen to manoeuver a submarine through side-scrolling levels displayed on the top screen, sinking enemy submarines, battleships and avoiding naval mines and depth charges as required. There are seven missions available, playable with different subs and difficulty modes, which usually involve goals such as eliminating enemy fleets or infiltrating enemy bases by reaching the goal in a time limit. Time Trials features the same gameplay style and controls, however the levels are shorter and are not connected to the story, instead being solely to achieve a fast time through a complex path. Periscope Strike mode is played after every successful mission or can also be played separately, or as part of Steel Commander. This mode sees the player moving the system to rotate a periscope to fire torpedoes at enemy ships. Steel Commander is playable against the CPU or a human opponent via Download Play. It is a strategy game in which the two players command a fleet of battleships and submarines and try to sink each other's fleet

Steel Diver Sub Wars:
In June 2013, it was announced that Nintendo was making a game which would be based on Steel Diver, to be released by March 2014. This was ultimately revealed to be titled Steel Diver: Sub Wars during the Nintendo Direct on February 13, 2014, which released after the event for the Nintendo 3DS. Sub Wars is a first-person game featuring a free-to-play online multiplayer mode and two levels of the single player campaign, with additional features and missions available to the paid version. Reviews have been mostly positive.

Note :All of this is from wiki because I didn't know what to write but some bits were edited by me since some bits are irrelevant

um no mean to necro post but bump