O'Byrne-class submarine

The O'Byrne-class submarines were a class of three submarines built for the French Navy from 1917 to 1920. They were originally ordered by the Romanian Navy, but were confiscated by the French government while still under construction. Three ships of the type were built between 1917 and 1920 at the Schneider shipyard in Chalon-sur-Saône. They were commissioned in the French Navy, serving in the Mediterranean Sea. The ships were removed from the Navy list between 1928 and 1935.

Construction and specifications
O'Byrne and her two sister ships (Henri Fournier and Louis Dupetit-Thouars) were ordered by the Romanian Government from the Schneider Shipyard in Gironde, being laid down in April 1917. However, Romania was forced out of the war in December 1917, when the construction of the three warships was at an early stage. The three submarines were subsequently completed for the French Navy, with larger bridges and conning towers. O'Byrne was the first to be launched (22 May 1919), followed by Henri Fournier (30 September 1919) and Louis Dupetit-Thouars (12 May 1920). They were completed and commissioned in 1921. Each of the three submarines had a surfaced displacement of 342 tons, measuring 52.4 meters in length, with a beam of 4.7 meters and a draught of 2.7 meters. Power plant consisted of two Schneider diesel engines and two electric motors powering two shafts, resulting in a surfaced top speed of 14 knots. Each vessel had a range of 1,850 nautical miles at 10 knots and a crew of 25. Armament consisted of four 450 mm torpedo tubes and one 47 mm deck gun.

Service
The three boats incorporated lessons from the French war experience, and thus proved to be reasonably successful. They served in the Mediterranean after World War I, but their careers were uneventful, and they were taken out of service before the start of World War II. Louis Dupetit-Thouars was stricken in November 1928 and her two sisters in August 1935.

Had O'Byrne been delivered to Romania upon completion, she would have become the first Romanian submarine. This role would be fulfilled by the Italian-built Delfinul in 1936.