Niterói-class (Mk 10)

The Niterói class is a series of seven frigates operated by the Brazilian Navy. Designed by the British shipyard Vosper Thornycroft as the Mk 10, the design is based on the Royal Navy's Type 21 frigate. Construction of the class spanned from 1972 to 1986. Vosper Thornycroft built four of the vessels in England, while the Rio de Janeiro Navy Arsenal constructed the remaining three in Brazil with British assistance. Six of the ships were configured as frontline warships, and the seventh, Brasil (U27), was built without weapons or sensors to serve as the navy's primary training vessel.

The frigates were built in two configurations: anti-submarine warfare (ASW) and general purpose (GP). The four ASW ships originally carried an Ikara missile launcher aft of the flight deck, while the two GP ships were equipped with a second 113 mm Mark 8 gun in that position. Propulsion is provided by a combined diesel or gas (CODOG) system driving two shafts, utilizing two Rolls-Royce Olympus TM-3B gas turbines and four MTU 16V 956 TB91 diesel engines. Each vessel features a helipad and hangar to support a Westland Super Lynx Mk.21B helicopter.

Between 1996 and 2005, the Brazilian Navy modernized the fleet under the ModFrag program. This program, delayed from its original 2001 target due to funding constraints and software sea trials, updated the ships' electronic and combat suites. The modernization removed the Ikara launchers from the ASW ships and established a standardized armament and sensor fit. The modernized weapons suite includes an Albatros launcher for eight Aspide surface-to-air missiles, a single 113 mm Mark 8 gun, two Bofors 40 mm guns, two twin Exocet anti-ship missile launchers, two triple tubes for Mark 46 torpedoes, and a double-barrel Bofors 375 mm Boroc anti-submarine rocket launcher. Modernized electronics consist of the SICONTA Mk 2 C3I system, Alenia RAN-20S air search radar, Terma Scanter surface search radar, Orion RTN-30X fire control radar, Saab EOS-400 optronic director, and a Krupp Atlas EDO-610E hull-mounted sonar. Electronic warfare capabilities include Cutlass B1W ESM, ET/SQL-1 ECM, and twelve 102 mm decoy launchers.

The lead ship, Niterói (F40), entered service in 1976 and was decommissioned in June 2019. The remaining vessels—Defensora (F41), Constituição (F42), Liberal (F43), Independência (F44), União (F45), and the training ship Brasil—remain active. Starting in 2025, the Niterói class will be gradually replaced in first-rank roles by the incoming Tamandaré-class frigates. Surviving Niterói-class vessels will be revitalized and transferred to patrol duties within the fleet.