O 19, laid down as K XIX, was an O 19-class submarine of the Royal Netherlands Navy that saw service during World War II. O 19, along with her sister ship O 20, were the first submarines in the world to be equipped with a submarine snorkel that allowed the submarine to run its diesel engines while submerged.

The submarine's keel was laid at the Wilton-Fijenoord shipyard in Rotterdam on 15 June 1936 as K XIX but was renamed O 19 at some point. The submarine was launched on 22 September 1938 and commissioned in the Dutch navy on 3 July 1939. After her commissioning the HNLMS O 19 was put into service by commander Lieutenant-on-sea 1 (LTZ 1) K. van Dongen on July 3, 1939, following a short training period. Three weeks later, on 25 July 1939, the new submarine was already on its way to the Dutch East Indies via the Suez Canal where the boat arrived on 13 September.

On 10 May 1940, the day the Germans invaded the Netherlands, the entire mobilization was proclaimed in the Dutch colony. Most Dutch warships, including the O 19, were used to protect allied merchant ships and to patrol the Indonesian archipelago. On May 31, 1941, the command of the Dutch submarine was taken over by LTZ 1 F.J.A. Knoops.

The submarine performed patrols and missions in the Pacific theater, sinking several Japanese vessels, attacking convoys and laying mines. In 1944 O 19 was placed under Task Force 71 of the United States Navy. On 16 November 1944 a Japanese coaster was spotted and sunk. On 8 July 1945, O 19 was en route to Subic Bay in the Philippines at a speed of 16 knots (30 km/h; 18 mph) when it struck Ladd Reef in the South China Sea. Unable to pull free of the reef, the crew of O 19 were rescued by the U.S. Navy submarine USS Cod. To prevent capture, O 19 was scuttled by both crews using explosives, torpedoes and gunfire.

The diesel engines for the HNLMS O 19 was built under the license of the Swiss Sulzer by the Koninklijke Maatschappij De Schelde in Vlissingen. It had 40 mm Bofors guns, which could be stored in watertight compartments in front of and behind the command tower, just like the O 12-class submarines. O 19 was also equipped with noise pulses from Atlas Werke in Bremen, Germany, which at that time were considered the best in the world. In 1943, during a major maintenance period in Great Britain, the noise spanner of O 19 was replaced by an Asdic system of type 120B.

Ships sunk by O 19.

Date	Ship name	Nationality/Type	Tonnage (GRT)	Fate
10 January 1942	Akita Maru	Japanese freighter	3817	Sunk
15 January 1942	Tairu/Taieryu Maru	Japanese ?	4944	Sunk
10 September 1944	Korei Maru	Japanese merchant	599	Sunk
16 November 1944	Kaishin Maru No.2	Japanese coaster	150	Sunk
9 January 1945	Shinko Maru No.1	Japanese auxiliary gunboat	935	Sunk
10 April 1945	Hosei Maru	Japanese merchant tanker	676	Sunk

• Horneman, Gerard D. (2015). Hr. Ms. O 19; 3 juli 1939 tot 8 juli 1945. Den Helder: Traditiekamer Onderzeedienst.

• Kiepe, P.C. (August 1992). "Patrouilles Hr.Ms. O-19 (III)" (PDF). Klaar Voor Onderwater (in Dutch). No. 40. Den Helder: Onderzeedienst Reünistenvereniging. pp. 10–13.

• Video of USS Cod sinking O 19
• IWM Interview with survivor Elke Scholte

8°40′N 111°40′E / 8.667°N 111.667°E / 8.667; 111.667