Morski Związkowy Klub Sportowy Arka Gdynia (, ) is a professional football club based in Gdynia, Poland, that plays in the Ekstraklasa after winning the 2024–25 I liga. The club was founded as Klub Sportowy Gdynia in 1929.
In 1949, Rybacki Klub Sportowy ("Fishermen Sports Club") MIR was formed. Three years later, its name was changed to Klub Sportowy Kolejarz-Arka Gdynia. In 1953, the team for the first time won promotion to the third level of Polish football. In 1959, Arka's U-19 became Polish runner-up, and in 1960, after a dramatic game vs. Hutnik Kraków, Arka won promotion to the Second Division.
In 1964, Arka merged with Doker Gdynia, to form Morski Związkowy Klub Sportowy (MZKS; "Maritime United Sports Club") Gdynia. In 1972, its name was changed into Arka. Two years later Arka won promotion to the Ekstraklasa. Relegated after one year, Arka returned to the top level in 1976. In 1979 Arka, managed by Czesław Boguszewicz, became the first team from Polish Baltic Sea coast to win the Polish Cup. In the final game, which took place in Lublin, Arka beat Wisła Kraków 2–1. In its UEFA Cup Winners' Cup debut, Arka lost to Bulgarian side PFC Beroe Stara Zagora (3–2, 0–2).
In 1982, Arka was relegated from the top level, to return there in 2005. In the 1982 World Cup in Spain, Arka's Janusz Kupcewicz was among top players of Polish national team, which won bronze medal.
In the 1980s and 1990s, Arka played either in the third or second division, with a number of promotions and relegations. In 2001, after six years in the third level, Arka again won promotion to the second division, and in 2005, the team returned to Ekstraklasa.
In 2011, the City of Gdynia completed the construction of a new Stadion GOSiR, located on Olimpijska Street. On 19 February 2011, Arka tied 1–1 with Beroe Stara Zagora in a friendly game to commemorate the opening of their new venue. That year, Arka were relegated from the top level.
In 2016, Arka was promoted to the top level again after taking first place in the I liga. Soon after getting promoted, Arka won the Polish Cup for the second time, and the Polish Super Cup twice: in 2017 and 2018.
The fans have an alliance with fans of Cracovia and Lech Poznań, and the three are known as "The Great Triad" ( Wielka Triada). Formerly, fans of Lechia Gdańsk, Śląsk Wrocław and Wisła Kraków also shared a friendship called "The Three Kings of Great Cities" ( Trzej Królowie Wielkich Miast) and any match between the two alliances was considered a big rivalry.tematy.gazeta.pl/W/2222,Wielka-Triada The alliance was dissolved in 2016, with Wisła Kraków turning hostile to Lechia Gdańsk and Śląsk Wrocław, and the fans of Wisła founding another alliance with Widzew Łódź, Ruch Chorzów and Elana Toruń, called WRWE, after the initials of its members. The only members who still are friends are Lechia Gdańsk and Śląsk Wrocław.
Arka fans maintain alliances with several other fans aside from Cracovia and Lech, many of them lasting now for decades: fans of Zagłębie Lubin (since 1983), Gwardia Koszalin (since 1989), and KSZO Ostrowiec Świętokrzyski (since 2004) are all considered good friends. The friendship with Polonia Bytom fans dates back to 1974, and is one of the longest friendships in supporter history which has survived to date.
The greatest rival or Arka is Lechia Gdańsk, a team with whom they contest the so-called Tricity Derby or Pomeranian Derby. Fans of both teams remain venomously hostile and since the early 1970s the history of games between Arka and Lechia is marked by riots and violence. Relations with another Gdynia football team Bałtyk Gdynia used to be friendly until the 1980s, when they turned hostile. Due to Bałtyk's successive relegations and their declining numbers of fans this rivalry is now of lesser importance.
| 1979–80 | UEFA Cup Winners' Cup | 1R | Beroe Stara Zagora | 3–2 | 0–2 | 3–4 |
| 2017–18 | UEFA Europa League | 3Q | FC Midtjylland | 3–2 | 1–2 | 4–4 (a) |
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