The Imperial Japanese Navy Air Service (IJNAS) was the air arm of the Imperial Japanese Navy (IJN). The organization was responsible for the operation of naval aircraft and the conduct of aerial warfare in the Pacific War.

William Francis Forbes-Sempill, 19th Lord Sempill,, was a Scottish peer and record-breaking air pioneer, who was later shown to have passed secret information to the Imperial Japanese military before the Second World War. Educated at Eton, he began his career as a pilot in the Royal Flying Corps, and then served in the Royal Naval Air Service and Royal Air Force during the First World War. In 1921, Sempill led an official military mission to Japan that showcased the latest British aircraft. In subsequent years, he continued to aid the Imperial Japanese Navy in developing its Navy Air Service.