Kancolle Kai

The gameplay is centered upon building squadrons composed of individual characters, "ship girls" (艦娘, kanmusu), represented as cards with different attributes, and then sending said squadrons out on missions. The player takes on the role of an admiral (提督, teitoku) and organizes their fleets in battle in order to win. Combat is largely automated, and manual actions by the player include micromanagement such as building and repairing. The player can organize up to four different fleets.

The player progresses through the game by advancing through maps, gaining experience points through grinding, obtaining new ship girls whilst repairing and resupplying existing ones, and fulfilling quests to obtain resources. New equipment can be crafted, allowing the ship girls to equip different armaments depending on the situation. Acquisition of new kanmusu by the player can occur via drops on map or via crafting, and is heavily RNG-based; randomization is also a key component of the battle mechanism, map progression and equipment development. Construction, resupply and repair of ships is reliant upon four types of resources, namely fuel, ammunition, steel and bauxite; these supplies will gradually increase automatically as time passes. Players can choose to engage in expeditions, sorties, and quests to further increase their supplies as well.

Whilst the original game does not have a particular storyline, and largely focuses on "gameplay", each of the official media works feature various settings with separate and differing canons. Not only do the stories differ, but also the depictions and interpretations of ship girls and the manner in which they engage in combat. The game does not strictly define anything relating to its setting, allowing for a greater diversity of secondary literary adaptation works which cater to different audiences, and more artistic freedom among secondary works which can approach the setting of Kantai Collection differently.

Kadokawa has not officially announced whether any secondary work is absolute canon, nor have they released significant quantities of canonical material, with some official works even contradicting one another. For instance, some manga anthology depictions show the ship girls as ship-sized giants, while other serialized manga show them as human-sized. The television animation explains the ship girls as humans born with the ability to possess the spirits of World War II warships, while within the Bonds of the Wings of Cranes light novel, the girls refer to themselves as actual warships, and that their origin is unknown.

Prior to Kantai Collection, the majority of games published by DMM.com were R-18+ adult online games. In an effort to attract customers from a wider audience, DMM.com experimented with Kantai Collection in partnership with Kadokawa Games; by November 2013, Kantai Collection accounted for 30-40% of DMM.com's total online game business.

Unlike other online games in Japan, Kantai Collection was designed with the intention of not requiring players to spend money or participate in "gacha" lotteries. The purpose of this stems from Kadokawa desiring a larger target market and to establish the game as a well-known name, eventually allowing for merchandising and sales of franchise works.

Due to the high popularity of the game within Japan, game operators created larger numbers of servers in early 2013 to cope with the influx of players. During August 2013, the number of new players spiked by 100,000 people within one week, to a total of 600,000 people, with 350,000 daily active players. By September 2013, it was reported that there were more than 800,000 players regularly active. The total number of players broke 1,000,000 on 9 October 2013.

As of April 2015, there were 3 million players. One commonly cited explanation behind the success of the game is that players are not forced to spend money to play, unlike other popular Japanese online games; the free-to-play nature of Kantai Collection makes in-game purchases optional, and not a necessity. It is estimated that on average, Kantai Collection players spend less money on the game compared to the popular Japanese games Puzzle & Dragons, The Idolmaster Cinderella Girls and Love Live! School Idol Festival.