Before Nissan's auto factory at Oppama, there was...

Nissan Motor Corporation has been in the news recently with reports about the possible impending closure of its large factory located in the Oppama District of Yokosuka City .... Of interest, the historical roots of Nissan's Oppama facility go back to the early 20th century, when it was an important air base for the Japanese Imperial Navy... 

横須賀海軍航空隊（横須賀海軍航空基地）

The Imperial Navy's first air corps was established on April 1, 1916.  It was originally a seaplane unit.  In addition to providing air defense for Yokosuka Naval District, it was responsible for educating and training air corps personnel, conducting practical tests on new aircraft, and researching the combat techniques of various aircraft models.  However, in February 1944, as the war situation became increasingly tense, it also began to be deployed in actual combat.

Around 1944, facilities began to be moved underground as a measure against air raids, and underground bunkers were dug like a network in the surrounding hills to store ammunition, fuel, supplies, etc.  Anti-aircraft positions were also constructed on the hills, and numerous anti-aircraft machine guns and anti-aircraft guns were installed.  Numerous aircraft bunkers (covered and uncovered) were also built around the runway, and the war ended with them in perfect condition.

According to records, the remaining aircraft at the end of the war were 14 Zero fighters, 12 Shiden, 3 Tenrai, 3 Gekko, 6 Ryusei, 7 Saiun, 1 Type 99 carrier bomber, 11 Ginga, 11 Suisei, 8 Tokai, 3 Type 96 land-based attack aircraft, 9 Type 1 land-based attack aircraft, 1 Zuiun, 3 Zero seaplanes, 1 Type 2 flying boat, 1 Type Zero fighter trainer, 3 Shiragiku, 3 Type 93 land-based training aircraft, 1 Type 90 No. 2 land-based training aircraft, 1 Type Zero transport, 3 Type 97 carrier attack aircraft, and 3 Tenzan, for a total of 108 aircraft.

Although it was only 30 years from its establishment until the end of the war, it was a central presence in the Naval Air Corps throughout, and in cooperation with the Aviation Technical Arsenal, it contributed greatly to the development of naval aviation technology.  In addition, all of the early pilots of the Japanese Naval Air Corps were from the Yokosuka Naval Air Corps, making it a historic and traditional aviation corps that formed the basis of the development of the aviation corps.

Most of the site has become the Nissan Motors Oppama Factory, and it is no longer accessible, and unfortunately very few historical structures remain.  All that remains are the underground bunkers that were constructed towards the end of the Pacific War.  Large horizontal underground bunkers still exist today in the hills surrounding the base - Nojima, Natsujima, Kaiyama, and Natakiriyama.  The super-large tunnel-style hangar for storing aircraft is particularly impressive.  Another notable feature is the number of stone monuments that have been erected to commemorate the historic air force.