The Sempill Mission was a British aeronaval technical mission led by Captain the Master of Sempill

William Forbes-Sempill, 19th Lord Sempill

William Francis Forbes-Sempill, 19th Lord Sempill was a British engineer. Before succeeding his father to the titles of Lord Sempill and Baronet of Craigevar in 1934, he was known by the title Master of Sempill....

 and sent to Japan in September 1921, with the objective of helping the Imperial Japanese Navy

Imperial Japanese Navy

The Imperial Japanese Navy was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes...

 develop its aeronaval forces. The mission consisted in a group of 29 instructors, headed by Colonel Sempill, and stayed in Japan for 18 months.

The Mission started training operation at the air base of Kasumigaura

Kasumigaura, Ibaraki

is a city located in Ibaraki, Japan. Kasumigaura was formerly a town in Niihari District and became a city on March 28, 2005 after merging with the neighboring town of Chiyoda, also from Niihari District. The city takes its name from the nearby lake, Lake Kasumigaura...

. The Japanese were trained on several new aircraft, such as the Gloster Sparrowhawk

Gloster Sparrowhawk

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, in various techniques such as torpedo bombing and flight control.

The Mission also brought the plans of the most recent British aircraft carriers, such as HMS Argus

HMS Argus (I49)

HMS Argus was a British aircraft carrier that served in the Royal Navy from 1918–1944. She was converted from an ocean liner under construction when the First World War began, and became the world's first example of what is now the standard pattern of aircraft carrier, with a full-length flight...

and HMS Hermes

HMS Hermes (95)

HMS Hermes was an aircraft carrier built for the Royal Navy. The ship was begun during World War I and finished after the war ended. She was the world's first ship to be designed and built as an aircraft carrier, although the Imperial Japanese Navy's was the first to be commissioned...

, which influenced the final stages of the development of the Japanese aircraft carrier Hōshō

Japanese aircraft carrier Hosho

Hōshō |phoenix]]") was the world's first commissioned ship that was designed and built as an aircraft carrier,The HMS Argus pre-dated Hōshō and had a long landing deck, but was designed and initially built as an ocean liner. and the first aircraft carrier of the Imperial Japanese Navy...

. Although the Hōshō was already launched by that time, she became the first aircraft carrier laid down as such in the world when she was commissioned in 1922, one year before the Hermes.