On June 11, 1944, Saipan, Tinian, and Guam were subjected to air raids by the American mobile task force. Furthermore, on the 15th, reports came in that the enemy had begun landing on Saipan. As the intentions of the US forces became clear, the Combined Fleet Headquarters issued Operation A-Gō, and the 1st Mobile Fleet immediately set sail toward the Marianas.

1st Mobile Fleet

- Second Fleet

   - 1st Strike Force

      - Battleships Yamato, Musashi, Nagato, Mutsu

      - Heavy cruisers Atago, Takao, Maya, Chōkai

      - Light cruiser Yahagi

      - Destroyers Yukikaze, Amatsukaze, Urakaze, Isokaze, Hamakaze, Tanikaze, Nowaki, Maikaze

      - Temporarily transferred from the Third Fleet

         - Shōhō (27 × A6Ms)

         - Zuihō (27 × A6Ms)

   - 2nd Strike Force

      - Battleships Kongō, Haruna

      - Heavy cruisers Kumano, Suzuya, Mogami, Mikuma, Tone, Chikuma

      - Light cruiser Noshiro

      - Destroyers Naganami, Tamanami, Fujinami, Hayanami, Okinami, Kishinami, Shiranui

      - Temporarily transferred from the Third Fleet

         - Chitose (27 × A6Ms)

         - Chiyoda (27 × A6Ms)

   - 3rd Strike Force

      - Battleships Yamashiro, Fusō

      - Light cruisers Abukuma, Kinu, Nagara

      - Destroyers Asagumo, Yamagumo, Michishio

- Third Fleet

   - Force A

      - Taihō (27 × A6Ms, 18 × D4Ys, 12 × B6Ns)

      - Shōkaku (45 × A6Ms, 18 × D4Ys, 12 × B6Ns)

      - Zuikaku (45 × A6Ms, 18 × D4Ys, 12 × B6Ns)

      - Heavy cruiser Myōkō

      - Light cruiser Agano

      - Destroyers Akizuki, Suzutsuki, Akigumo, Kazagumo, Asashimo, Hayashimo, Akishimo

- Force B

   - Akagi (36 × A6Ms, 18 × D4Ys, 12 × B6Ns)

   - Hiryū (36 × A6Ms, 9 × D4Ys, 12 × B6Ns)

   - Sōryū (36 × A6Ms, 9 × D4Ys, 12 × B6Ns)

   - Heavy cruiser Haguro

   - Light cruiser Isuzu

   - Destroyers Hatsuzuki, Wakatsuki, Kasumi, Suzukaze, Umikaze, Shiratsuyu, Shigure

- Force C

   - Jun'yō (36 × A6Ms, 12 × B6Ns)

   - Hiyō (36 × A6Ms, 12 × B6Ns)

   - Ryūhō (27 × A6Ms)

   - Battleships Ise, Hyūga (44 × D4Ys)

   - Light cruiser Tama

   - Destroyers Shimotsuki, Fuyuzuki, Harusame, Samidare, Hatsuharu, Wakaba, Hatsushimo

The 1st Mobile Fleet consisted of 13 aircraft carriers, 10 battleships, 12 heavy cruisers, 7 light cruisers, and 40 destroyers.

Among them, the Second Fleet's 1st Strike Force, the most powerful unit, relied on the battleships Yamato and Musashi with 46 cm guns, and the Nagato and Mutsu with 41 cm guns, as its core forces. The 2nd Strike Force was composed of fast ships, featuring the fast battleships Kongō and Haruna, along with six heavy cruisers. The 3rd Strike Force had slow battleships, Yamashiro and Fusō, as its main strength, and there were heated debates between the General Staff and the Combined Fleet Headquarters about whether to involve them in this battle. Due to the critical nature of the impending battle, their deployment was eventually decided.

Temporary additions to the 1st Strike Force included the Shōhō and Zuihō, while the 2nd Strike Force received the Chitose and Chiyoda. These units were not meant to protect the head of the Second Fleet but rather to divert enemy aircraft attacks from battleships, serving as decoys or damage-absorbing ships.

The mobile unit, the Third Fleet, was divided into three units: Force A, B, and C.

Force A comprised the aircraft carriers Taihō, Shōkaku, and Zuikaku, led by Vice Admiral Ozawa, flying his flag on the state-of-the-art armored carrier Taihō. Force B was composed of veteran carriers Akagi, Hiryū, and Sōryū, under the command of Vice Admiral Yamaguchi. Force C included the light carriers Jun'yō, Hiyō, and Ryūhō, along with the converted aviation battleships Ise and Hyūga. These carried the difficult-to-operate D4Y Suisei in addition to strengthening the air power of Force C. All the fighter planes were the new model Zero Model 52, and the bombers transitioned from the D3A to the Suisei, and the torpedo bombers upgraded from the B5N to the B6N Tenzan. Given the dire circumstances of the upcoming battle, many of the aircrews included instructors and staff from the training air groups.

With these forces, the 1st Mobile Fleet rushed to the battlefield of the Marianas. If the 1st Mobile Fleet were to be defeated, leading to the loss of the Marianas, Japan's defeat would become decisive. Therefore, in this battle, the Japanese forces were prepared to press the attack without considering their own losses and were even willing to sacrifice certain units if deemed necessary for the operation.