In June 1976, the Brazilian Navy submarine Humaitá (S-20) completed a naval transit from Ilhéus to Belém, spending over 195 hours submerged. The mission covered 1,203 nautical miles, of which 668 were traveled submerged.
The Humaitá’s journey was part of a larger operation that totaled 3,396 nautical miles, 231 hours submerged, and 19 days at sea.
Operational Benchmarks of the S-20
The Humaitá was built by the British shipyard Vickers Shipbuilding and belonged to the Oberon class, alongside the Tonelero and Riachuelo. With a length of 90 meters and a displacement of 2,420 tons when submerged, the vessel had eight 533-millimeter torpedo tubes and a planned crew of 70 officers, non-commissioned officers, and sailors.
During the Ilhéus-to-Belém leg, the submarine traveled 668 nautical miles submerged, more than half of that leg’s total distance. The more than 195 hours submerged refers to cumulative time underwater during the transit, not necessarily one uninterrupted dive.
| Metric | Mission Detail |
|---|---|
| Total Mission Distance | 3,396 Nautical Miles |
| Total Time at Sea | 19 Days |
| Cumulative Submerged Time | 231 Hours |
| Total Submerged Distance (Ilhéus to Belém) | 668 Nautical Miles |
Evolution of Brazil’s Submarine Presence
The 1976 navigation formed part of the history of the Brazilian Navy’s submarine presence in waters near the mouth of the Amazon River. During that period, the American-origin Amazonas (S-16) also operated in the region. Decades later, the Tupi (S-30) continued that activity, and more recently the Humaitá (S-41), of the Riachuelo class, was deployed during Operation Atlas 2025.
The original Humaitá (S-20) remained in service until April 1996. Its official record lists more than 14,000 hours submerged and 151,258 nautical miles traveled during its career in the Brazilian Navy.
