Heian Maru

At over 11,000 gross tons, the Heian Maru is the largest ship on the floor of Truk Lagoon. She began in 1930 as a comfortable NYK liner on the Yokohama–Seattle run, her name lettered on the bow in both English and katakana — both still readable underwater, which never stops being strange. Requisitioned in 1941 and converted to tend the submarines of the Sixth Fleet, she was serving as their flagship depot ship when Operation Hailstone caught her at anchor. Bombed and set ablaze across the raid's two days, she rolled onto her port side as she sank. Her scale defines the dive: swimming her length is a full tank's work, past long-lance torpedoes lying in racks, spare periscopes bundled like lumber, and cavernous holds. Submariners' stores went down with submariners' comrades; remains have been found within, and she is dived as the war grave she is.

沈没の経緯: Bombed and burned during Operation Hailstone, 17–18 February 1944.

コンディション: Substantially intact for her size; interior decks are slowly shedding fittings as steel fatigues.

洞窟貫通（ペネトレーション）: Full With Training. Passageways and holds are spacious but rotated ninety degrees, which disorients; wreck training and a lagoon guide are the standard. 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: Advanced Open Water; wreck training for interiors

流れ（カレント）: Mild · 透明度: 15–30 m

海洋生物: Encrusting corals and sponges shingle the upturned hull, fusiliers stream along the promenade rails, and eagle rays pass over the sand.

危険生物・リスク: Sideways geometry confuses navigation inside; silt banks lie deep in the holds; torpedoes and munitions are live and untouchable.

Chuuk lagoon monument protection; state dive permit/fee applies.

Human remains rest aboard — enter with restraint and take only photographs of the ship, never of the dead.

Removal of any object is illegal under Chuuk state law.