The Atlantean 5.1"/55 (130 mm) gun is the mainstay of the Atlantean navy. It replaced the 4" gun in 1928 the main armament on destroyers and as a secondary armament on newer battleships, aircraft carriers and some classes of heavy cruiser. The gun itself has changed little with only slight refinements to the breach mechanism. The biggest changes have been made in the gun mounts, turrets and hoists. The first guns were used on the H class destroyers in shielded ring base mounts hand loaded with a vertical breach block, while the latest guns are mounted in halfdeck turrets with improved hoists, rammers and loading mechanisms.
The 5.1" is made up of the following marks:
Mk 1/45 1928, shielded mount hand loaded, 12-16 rounds per minute
Users-
Atlantis: H class
Chile: Chiloe class CVL
Mk 2/45 1932, fully enclosed turret, manually loaded, power rammed, 15-20 rounds per minute
Users-
Atlantis: I/J/K class DD
Chile: Capitan Thompson, Almirante Lynch class DD
Colombia: Santander class BC, Cali class AC, Almirante Pidila/Buenaventura class CLAA, Pereira/Tunja/Yopal class CLAA, San Augustine/San Jacinto class DD
Mk 3/55 1936, fully enclosed half deck turret, manually loaded, power rammed, 18-20 rounds per minute
Users Atlantis: Neptune class BB, Vengeance class BC, Arcturus class CV, Nereus class CV, Perseus class CA, Medusa/Nemesis/Zerberus class CLAA, L,M and N class destroyers, Venture/Venerable class Tenders
Brazil: *Turrets only* Arara/Santos de Espar class DD's
Bulgaria: Sofia II class BB, Drazki class DD
Chile: Libertad, Patria class CV, Blanco Encalada, Capitan Prat class BC, Constitución class CA, Concepcion, Voluntario, Temerario, Capitan Eyzaguirre, Aldea class DD, Disembarkment of Pisagua class LSD
Colombia: Almirante Brión class CA, San Roque class DD
Irland: LÉ Connacht class DD
Turkey: Hizar Reis, Murat Reis class CA, Yar Hisar class DD
Mk 4/55 1940, fully enclosed half deck turret, autoloaded and rammed, 20-22 rounds per minute, first trialed in Chilean Battle class DD
Users-
Atlantis : Helios class CV, Phoenix class CA, Archer class DD
Bulgaria: Neustrashimi, Kyustendil class DD
Chile: Arica and Concepción class CLAA, Battle class DDL, Almirante Williams, Cerro Vitz Roy, Almirante Simpson, Chacabuco, Bolados class DD
may not be accurate for Chilean info*