Instructor Captain Oswald Thomas Tuck (1 September 1876 – 26 February 1950) was a naval officer and teacher of Japanese. He served as a naval instructor in navigation and Japanese and later translated a confidential history of the Russo-Japanese War. He retired as an Instructor Captain in the Royal Navy but was recalled to duty in 1941 to run the Bedford Japanese School, which trained young men and women for work at Bletchley Park.

Tuck was the fourth son and fifth and last child of Henry Barber Tuck (1834–1906) and Harriott Tuck (née Horn (1837–1907). He attended the Royal Hospital School, Greenwich, leaving in January 1892 with the highest results in his class. While still at school he applied to Sir Sir William Christie, the Astronomer Royal, to take the examination to become a 'computer' at the Royal Observatory. He was the only candidate but his examination papers were judged excellent. He began work at the Royal Observatory, Greenwich, on 11 January 1892, at the age of 15. As a 'supernumerary computer', it was his job to turn observational data into a standard form. In 1893 he was certified as competent in the use of the transit circle (a device similar to a meridian circle used to time the transit of stars across the local meridian) and the use of the Sheepshanks Equatorial telescope. In July 1894, after having worked at the Royal Observatory for two and half years, he resigned his position to enter the employment of the Royal Navy as a teacher. He must have continued his astronomical studies for, in November 1895, at the age of 19, he was the youngest person ever elected a Fellow of the Royal Astronomical Society. He was proposed by Edward Walter Maunder, who was a senior member of staff at the Royal Observatory. He left the Royal Astronomical Society in 1901.

In 1894 he was appointed to teach astronomy and navigation on HMS Conway, a training ship stationed on the Mersey near Liverpool. During this period of his life he was going to the theatre and to concerts in Liverpool and was also taking London University external examinations at University College Liverpool (now the University of Liverpool). In 1898 he passed Intermediate Science and applied to become a Naval Instructor. In June 1899 he received an appointment as a Naval Instructor, and was sent to East Asia. This was an unusual appointment in the sense that most Naval Instructors had a university degree. He served first in HMS Goliath, a pre-Dreadnought battleship launched in 1898 and based on the China Station, and later in HMS King Alfred, an armoured cruiser which was the flagship of the China Station.

In June 1904, four years after Tuck had begun learning Japanese on his own initiative and two years after the Anglo-Japanese Alliance had come into force, the Admiralty made special arrangements for the study of Japanese by naval officers, allowing up to a year's residence in Japan. In August Vice-Admiral Sir Gerard Noel, Commander-in-Chief of the China Station, wrote to Sir Claude Maxwell MacDonald, the first British ambassador to Japan, seeking the services of a ‘suitable and reliable Instructor in the Japanese language for service with the British China Squadron’, possibly a ‘suitable retired Japanese Naval Officer, who has perhaps been wounded in the war and would be glad of a little financial assistance’. In February 1905, Macdonald replied to Noel to say that Baron Komura Jutarō, the Minister of Foreign Affairs, had been unable to find a suitable person. By this time Tuck was living in Japan and studying the language full-time, although he was finding the expenses involved much greater than he had expected. Later in 1905 Sir Claude MacDonald instructed John Harington Gubbins, who had been Japanese Secretary in the British Legation for many years and had a good command of Japanese, to examine Tuck on his knowledge of Japanese. Gubbins reported in September that Tuck had gained full marks in colloquial and more than 75% for each of the two written papers, and that he had a good knowledge of Chinese characters. ‘A little further study of newspapers, and a course of instruction in what is known as official dispatch style, would, I think, enable Mr. Tuck to attain the standard required for interpreters in the Japan Consular Service', he concluded. In December Tuck received a certificate stating that he had passed the examination for Interpreter in Japanese and a few days later received appointment as Interpreter in Japanese on HMS King Alfred. In February 1906 Vice-Admiral Noel wrote to Tuck and forwarded to him extracts from an Admiralty letter dated 25 October 1905, which stated that ‘it would be a convenience if the services of Mr. Oswald Tuck could be utilized in connection with the instruction in the Japanese language of Naval Officers on the China Station, having regard to his special qualifications for such work’. And in 1907 the Admiralty wrote to express their appreciation for Tuck's translation of a diary by a Russian officer serving on the Russian battleship Oryol. It was clear that Tuck's command of Japanese was now appreciated by the Admiralty.

In 1908 he was appointed as assistant to the British Naval Attaché, Captain Dundas, in Tokyo. On 13 January he received a letter from Captain (Later Admiral Sir) Herbert King-Hall, Assistant Director of the Naval Intelligence Division in the Admiralty, suggesting that he return to England for permanent employment in the Naval Intelligence Division. This indicates that Tuck was already well thought of in the Navy, and at the end of the year he decided to accept the appointment offered to him, and left Japan for the last time in his life.

He returned to England in 1909 and was attached to the Naval Ordnance Department of the Admiralty while nominally assigned to HMS President. He was eventually promoted to Instructor Commander, with seniority dating from 1913. During the Great War his appointment was described as, 'for duty with the Naval Staff, lent to the Historical Section of the War Cabinet'. By 1921 he was Head of the Historical Section in the Training and Staff Duties Division of the Admiralty. He remained an Instructor Commander until he retired in 1924, when he was given the rank of Instructor Captain: he was the only one without a university degree. He continued to work on the volumes of the official naval history of the Great War until 1937, in the capacity of Technical Assistant in the Historical Section of the Committee of Imperial Defence. On the strength of his work as a historian, in 1934 he applied to the University of Cambridge when the position of Vere Harmsworth Professor of Imperial and Naval History fell vacant, but it was in the end offered to one of his referees, Admiral Sir Herbert Richmond (1871–1946).

Tuck first visited Japan in November 1900 and was immediately enthusiastic. He wrote to his future wife: 'I take back every word I have said against the Japanese; they are the most delightful people on the face of the earth. It is a perfect joy to go into a shop for the mere object of talking to the owner. Everyone has the most engaging way with them – and all merely for politeness, not for the sake of what they can get out of you.' He started 'struggling with Japanese' right away and by February of the following year he was already confident enough to write, 'I can now talk well enough to go about the country alone and I shall certainly do so when we get there; being able to eat the food of the country renders me quite independent.'.

In 1902, when HMS Goliath was stationed in Hong Kong, he continued to extend his knowledge of Japan by reading Lafcadio Hearn's Glimpses of unfamiliar Japan (1894) and The Mikado's Empire by William Elliot Griffis (1876). He was also practicing his Japanese with a young man named Tajima, and asked the Japanese consul to help find him a teacher. In May HMS Goliath put in to Yokohama and Tuck received the Admiral's permission to rejoin the ship at Nagasaki after travelling by train and boat to Beppu in Kyushu and then walking from there to Nagasaki. In the event he had to retrace his steps and rejoin the ship at Miyajima. By October, after a spell at Weihaiwei, the Goliath returned to Yokoyama and Tuck applied for leave to remain in Japan for four months to learn Japanese. He was permitted to bring on board a young Japanese man as a servant, Kondō Takezō: with Kondō he began learning Chinese characters. The Admiral rejected his application, saying that his job was to instruct midshipmen. He reapplied, and forwarded to the Admiral with a letter from H. Kirino, the acting Japanese consul in Hong Kong, saying, ‘I do hereby certify that Mr. Oswald T. Tuck RN of HMS Goliath can now speak Japanese tolerably well and after one year’s exclusive study there is no doubt of the possibility of his expert talking of the same.’