The Spanish Navy’s S-81 “Isaac Peral” submarine has joined NATO operations in the Mediterranean Sea for the first time, taking part in Operation Sea Guardian, the alliance’s maritime security mission aimed at enhancing situational awareness and protecting critical sea lines of communication.
According to NATO Maritime Command, the milestone reflects continued cooperation among allied naval forces. Operation Sea Guardian focuses on counter-terrorism, freedom of navigation, and maritime situational awareness across the Mediterranean region.
Designed and built entirely in Spain by Navantia, the S-81 is the first in a new generation of conventional submarines featuring advanced automation and an anaerobic propulsion system. The vessel’s third-generation Air-Independent Propulsion (AIP) system, known as BEST (Bio-Ethanol Stealth Technology), uses a bioethanol reformer to produce hydrogen, which combines with oxygen in a fuel cell to generate electricity—allowing the submarine to remain submerged for up to three weeks without surfacing.
Measuring approximately 80 meters in length and 7 meters in diameter, with a submerged displacement of around 3,000 tons, the S-81 can exceed speeds of 19 knots and dive deeper than 300 meters. Operated by a crew of 32 sailors and 8 additional personnel, it is equipped with a combat management system developed by Navantia Sistemas in collaboration with Lockheed Martin.
The S-81 is also notable within NATO and the EU as one of the few conventional submarines capable of launching tactical land-attack missiles, providing Spain with expanded operational flexibility in joint maritime missions.
📌 The Spanish Navy’s S-81 “Isaac Peral” submarine has joined NATO operations in the Mediterranean Sea for the first time.
🔗 https://t.co/dyG2TR8mW1@NavantiaOficial pic.twitter.com/5TfPXULmil
— Defensehere (@defensehere_en) October 22, 2025