Capitan O'Brien-class submarine (1928)

The Capitan O'Brien class were three submarines built for the Chilean Navy in the late 1920s. Designed and built in the United Kingdom, they were a modified design of the contemporary British Odin-class submarines. The lead boat, CHILEAN SUBMARINE Capitan O'Brien, was launched on 2 October 1928 and the other two on 15 January 1929. All three submarines entered service in 1929. The three vessels remained in service until being discarded in 1957–1958.

Background and design
The Capitan O'Brien class were three submarines constructed to a modified design based on the British Royal Navy's Odin-class submarine. The Odin class was the Royal Navy's leading submarine design in the post-World War I era, equipped with strengthened pressure hulls and fuel carried in the ballast tanks to improve rapid diving. They had extended surface range. The Capitan O'Briens measured 260 ft long between perpendiculars with a beam of 28 ft and a draught of 13 ft. They had a displacement of 1540 LT while surfaced and 2020 LT submerged. The submarines were propelled by two shafts powered by two Vickers diesel engines creating 2750 bhp while surfaced and two electric motors creating 1300 hp while submerged. This gave them a maximum speed of 15 kn surfaced and 9 kn submerged. The builder's photograph of Capitan Simpson gives the dimensions as 272 ft long overall with a beam of 27 ft and a draught of 16 ft with a surface speed of 15 knots and 9.5 knots submerged.

The Capitan O'Briens had a large conning tower that stretched one-third of the deck and mounted the 4.7 in/45 deck gun in a turret. The submarines were also armed with eight 21 in torpedo tubes, with six located in the bow and two in the stern. The subs carried 14 torpedoes. Each submarine had a complement of 54 personnel.