It is for this reason that the Tridente class is commonly designated as the U 209PN.

The class and its ships are the first to not be named after marine animals, thus breaking a tradition retracing back to 1913, when the first submarine entered service with the Portuguese Navy.

These batteries may be charged while submerged by "fuel-cells" (inverse electrolysis) for which, this submarine carries a huge supply of liquid oxygen and hydrogen.

Also, and solely as a second solution for recharging the batteries, this submarine carries two powerful diesel-electric generators (1,000 KVA) for use only when surfaced, or at snorkel depth.

Submerged, from Lisbon, Portugal, submarines of the class may reach the Cape of Good Hope and return, in 15 days.