HIJMS Nagato

When she commissioned in 1920, Nagato was the first battleship in the world to mount 16-inch guns, and for two decades she was the pride of the Combined Fleet. It was from her flagship radio room, at anchor in home waters, that the coded order confirming the Pearl Harbor attack went out in December 1941. She survived Leyte Gulf and finished the war as Japan's last operational battleship, battered at Yokosuka. The Americans took her to Bikini for Operation Crossroads, moored her close to the bomb, and she absorbed both blasts; after Baker she settled slowly for five days and rolled over unobserved during the night of 29–30 July 1946. She rests upside down, her four great screws at technical-diving depth and her 16-inch guns beneath the overturned hull. For wreck divers she is a pilgrimage: the physical remainder of the fleet that began the Pacific war, reachable only by expedition, in a lagoon whose nuclear history is briefed alongside the dive plan.

沈没の経緯: Damaged by the Baker atomic test and sank at night on 29–30 July 1946.

コンディション: Structurally sound but inverted; the superstructure is crushed beneath the hull. Residual radioactivity at diver depths is low on modern surveys — a briefing point, not a barrier.

洞窟貫通（ペネトレーション）: Limited. Passages beneath and inside the inverted hull are for experienced technical teams; the casing spaces silt heavily and exits are unobvious. オーバーヘッド環境への進入には専門的なトレーニングが必要です——最低限、レック・ダイビング認定資格が必要で、完全貫通には技術的なレック・トレーニングが求められます。

推奨ライセンス: Technical/trimix certification

流れ（カレント）: Mild · 透明度: 20–35 m

海洋生物: Trevally and grey reef sharks patrol the hull's shadowed flanks; growth is modest under the dark overhangs, richer along the propellers.

危険生物・リスク: Depth from the first minute of the dive, overhead environment, remoteness from medical care, and wartime munitions still aboard.

Part of the Bikini Atoll UNESCO World Heritage Site; access only through authorized expeditions with Bikinian and Marshallese approval.

Every object aboard is heritage of two nations — removal is prohibited.