She set world depth records, competing against a more refined version of her design, the Trieste.

[1] After damage to the FNRS-2 during its sea trials in 1948, the Belgian Fonds National de la Recherche Scientifique (FNRS) ran out of funding, and the submersible was sold to the French Navy, in 1950.

She was subsequently substantially rebuilt and improved at Toulon naval base, and renamed FNRS-3.

[3] On 15 February 1954, she made a 4,050 metres (13,290 ft) dive 160 miles off Dakar, Senegal, in the Atlantic Ocean, beating the 1953 record of Auguste Piccard, set by the Trieste, by 900 meters.

[2][4][5] Piccard's record had been set by reaching the floor of the Mediterranean off Naples, a depth of 10,392 feet (3,167 m).