Akagi ( "Red Castle") was an aircraft carrier

Aircraft carrier

An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...

 of 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...

 (IJN), originally begun as an . She was converted while still under construction to an aircraft carrier under the terms of the Washington Naval Treaty

Washington Naval Treaty

The Washington Naval Treaty, also known as the Five-Power Treaty, was an attempt to cap and limit, and "prevent 'further' costly escalation" of the naval arms race that had begun after World War I between various International powers, each of which had significant naval fleets. The treaty was...

. Following Japan's renunciation of the Treaty, the ship was rebuilt from 1935 to 1938 with her original three flight deck

Flight deck

The flight deck of an aircraft carrier is the surface from which its aircraft take off and land, essentially a miniature airfield at sea. On smaller naval ships which do not have aviation as a primary mission, the landing area for helicopters and other VTOL aircraft is also referred to as the...

s consolidated into a single, enlarged flight deck and an island superstructure.

Akagis aircraft participated in the Second Sino-Japanese War

Second Sino-Japanese War

The Second Sino-Japanese War was a military conflict fought primarily between the Republic of China and the Empire of Japan. From 1937 to 1941, China fought Japan with some economic help from Germany , the Soviet Union and the United States...

 in the late 1930s, and she became the flagship

Flagship

A flagship is a vessel used by the commanding officer of a group of naval ships, reflecting the custom of its commander, characteristically a flag officer, flying a distinguishing flag...

 of the First Air Fleet

1st Air Fleet of the Imperial Japanese Navy

The Imperial Japanese Navy at the beginning of World War II contained the world's largest carrier fleet. At the centre, was the 1st Air Fleet which was a grouping of naval aircraft and aircraft carriers...

 or Kido Butai (Striking Force) in early 1941.