BREAKING NEWS: Brazil enters final phase of nuclear submarine program with launch of Almirante Karam S43.

The Brazilian Navy marked two major milestones at the Itaguaí Naval Complex during the PROSUB25 ceremony, showcasing the armament display of the Tonelero S42 and the christening and launch of the Almirante Karam S43. These achievements close the conventional construction phase and shift full focus to Brazil’s first nuclear-powered attack submarine, the Álvaro Alberto.

The Brazilian Navy used the PROSUB25 ceremony on November 26, 2025, at the Itaguaí Naval Complex to highlight two defining steps in its submarine program, presenting the Tonelero S42 as it entered the armament phase and formally christening and launching the Almirante Karam S43. Officials noted that the delivery path for these submarines concludes Brazil’s conventional construction stage and clears the way for full attention on the Álvaro Alberto, the nuclear-powered attack submarine regarded as the most advanced chapter of the PROSUB effort.
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Brazilian Navy launches the Almirante Karam (S43) submarine at the Itaguaí Naval Complex on November 26, 2025, marking the final conventional unit of the PROSUB program before the transition to nuclear submarine production. (Picture source: Brazilian Navy)

PROSUB, Brazil’s most ambitious naval modernization initiative, was established in 2008 through a strategic partnership with France’s Naval Group. The program aims to deliver a fleet of modern submarines, transfer critical technologies, build a sovereign naval industrial base, and prepare for nuclear propulsion capability. The creation of the Itaguaí Naval Complex and Itaguaí Construções Navais (ICN) enabled Brazil to move from imports to the independent design and construction of submarines on its own territory.

The new conventional submarines, the Riachuelo (S40), Humaitá (S41), Tonelero (S42), and Almirante Karam (S43), are based on the French Scorpène-class but have been extensively adapted to Brazilian specifications and reclassified as the S-BR class. These diesel-electric attack submarines measure 71.6 meters in length and displace about 1,870 tons submerged. Each is fitted with six 533 mm torpedo tubes capable of launching French F21 heavyweight torpedoes and SM39 Exocet anti-ship missiles. The platform is optimized for stealth, extended underwater endurance, and operations across Brazil’s vast maritime zone. The S-BR class features an advanced sonar suite, electronic warfare systems, and a combat management system tailored to Brazilian Navy doctrine and operational conditions.

The christening and launch of Almirante Karam mark the closing chapter of the conventional segment of PROSUB. The program now enters its most technologically complex phase with the construction of the SNCA Álvaro Alberto, Brazil’s first nuclear-powered submarine. Designed to displace over 6,000 tons submerged and exceed 100 meters in length, Álvaro Alberto will be conventionally armed with torpedoes and anti-ship missiles. Its primary advantage lies in its nuclear propulsion system, developed indigenously under the supervision of the Navy's Technological Center in São Paulo and the National Nuclear Energy Commission. This system will grant the submarine unlimited submerged endurance and extended operational range, transforming Brazil’s ability to conduct persistent, long-distance naval patrols across the South Atlantic and beyond.

As of late 2025, the Brazilian Navy operates four diesel-electric submarines. Two of these belong to the new S-BR class: Riachuelo and Humaitá, both in active service and armed with SM39 Exocet missiles and F21 torpedoes. The legacy fleet includes the Tupi (Type 209/1400), fitted with eight 533 mm tubes and Mk 48 heavyweight torpedoes, and the Tikuna (Type 209/1450), equipped with eight single 533 mm tubes and Mk 24 Tigerfish torpedoes. Older Tupi-class units Tamoio, Timbira, and Tapajó have been withdrawn or placed in reserve. Once Tonelero and Almirante Karam complete sea trials and join the fleet, Brazil will field four modern S-BR class submarines alongside two remaining German-origin platforms, pending the SNCA's eventual commissioning.

With the full realization of PROSUB, including the Álvaro Alberto, Brazil will operate a six-submarine fleet combining advanced conventional boats with nuclear-powered endurance and strategic mobility. This force structure positions the Brazilian Navy as the most capable undersea force in Latin America and the Southern Hemisphere. Brazil's submarine command, Força de Submarinos (ForSub), based at the Submarine Base Admiral Castro e Silva in Rio de Janeiro, now oversees a fleet capable of sustaining long-term deterrent patrols, defending offshore oil infrastructure, securing sea lines of communication, and conducting joint operations with partner navies.

The PROSUB initiative has generated strategic, industrial, and technological benefits beyond its immediate military goals. The program has mobilized over 40 Brazilian defense and engineering companies and created thousands of high-skilled jobs. It has also accelerated research in nuclear propulsion, systems integration, metallurgy, and underwater warfare. The SNCA’s development marks the first time a nation in the Southern Hemisphere will operate a domestically developed nuclear-powered attack submarine, placing Brazil alongside only a handful of global powers with this capability.

Brazil’s future submarine fleet reflects a broader doctrine shift that recognizes the strategic value of the South Atlantic in global maritime affairs. As competition over resources intensifies and the geostrategic importance of maritime chokepoints increases, Brazil's undersea capabilities are becoming central to its national defense policy. The ability to conduct sustained, covert patrols and project naval presence across 3.5 million square kilometers of maritime jurisdiction ensures that Brazil will remain a decisive actor in regional security.

With Almirante Karam launched and Álvaro Alberto underway, Brazil redefines its submarine capabilities. PROSUB now stands as a symbol of strategic autonomy and ambition, reinforcing Brazil’s role among major naval powers.