Brazilian Navy tests submarine Tonelero stability in first static immersion near Rio de Janeiro.

According to information published by the Brazilian MoD on October 30, 2024, the Brazilian Navy’s S42 submarine Tonelero undertook its first static immersion test near Itacuruçá Island, Rio de Janeiro. This procedure aimed to verify the stability of the S42 both on the surface and while submerged.
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The Brazilian Navy's Riachuelo-class submarine Tonelero. (Picture source: Brazilian MoD)

Commander Eduardo Tavares Santos, captain of the Tonelero, credited the success of this mission to intensive simulator training that fully prepared the crew. He shared that the test went smoothly as planned and without any issues. Looking ahead, he outlined the next stages in the S42’s operational readiness journey, expecting surface tests to be completed by the end of the year. This will lead to Dynamic Immersion trials, a first battery recharge while submerged using a snorkel to intake air without surfacing, and a Deep Dive Immersion to examine structural hull integrity.

The static immersion process involves the controlled filling of the submarine’s ballast tanks until it is fully submerged, without propulsion. By adjusting weights along the vessel, engineers observe the platform’s stability under various angles, collecting vital longitudinal and transverse stability data. The test also verifies the water levels in internal compensation and trim tanks, precisely calculating the submarine’s displacement under submerged conditions.

Future evaluations will include additional system installations and commissioning, followed by another static immersion to assess the final weight configuration of the Tonelero.

The Tonelero belongs to Brazil’s Scorpène-class, a French-designed series adapted to the specific operational requirements of the Brazilian Navy. Larger than the original model, the Tonelero is over 71 meters long and has a submerged displacement of 1,870 tons.

Launched in March 2024 at the Itaguaí Naval Complex, Tonelero is the third conventionally powered diesel-electric submarine produced in Brazil under the Submarine Development Program (PROSUB), a strategic partnership with France dating back to 2008. This program aims to enhance Brazil's naval capabilities with technology transfer in the defense sector.

Alongside Tonelero, the Brazilian Navy has already inducted two submarines, Riachuelo (S40) and Humaitá (S41). Another submarine, initially named Angostura (S43) and recently renamed Almirante Karam in honor of a former Navy Minister, is also scheduled for delivery. Additionally, the program includes the construction of the conventionally armed nuclear submarine Álvaro Alberto.