Hashirajima Anchorage

Hashirajima Anchorage (柱島泊地, Hashirajima Hakuchi) was the principal fleet anchorage of the Imperial Japanese Navy's Combined Fleet (聯合艦隊) during the Pacific War. Located in the southern reaches of Hiroshima Bay in the Seto Inland Sea, the anchorage extended across the waters surrounding Hashira Island (柱島), approximately 26 kilometres southeast of Iwakuni and 30–40 kilometres southwest of Kure Naval Base. The island itself, the main island of the Hashirajima Islands (柱島群島), covers 3.12 square kilometres.

The anchorage's strategic value lay in its sheltered deep-water position within the Inland Sea, offering natural protection from submarine attack and open-ocean observation while remaining accessible to the major naval facilities at Kure, Hiroshima, and Etajima. When warships did not require dockyard repairs, they anchored at Hashirajima to free up limited pier space at Kure. The anchorage could accommodate the entire Combined Fleet, including the largest battleships ever built.

Combined Fleet Headquarters

Hashirajima served as the de facto operational headquarters of the Combined Fleet for much of the war. Battleship Nagato, which had resumed duty as Combined Fleet flagship in October 1941, was moored here when Admiral Yamamoto Isoroku issued the fateful coded signal "Niitaka Yama Nobore 1208" (ニイタカヤマノボレ一二〇八 — Climb Mount Niitaka, 1208) on 2 December 1941. This order, transmitted from Nagato's bridge at Hashirajima, instructed Vice Admiral Nagumo Chūichi's First Air Fleet (Kido Butai), already underway in the North Pacific after departing Hitokappu Bay on 26 November, to execute the surprise attack on Pearl Harbor scheduled for 8 December (Japan time) / 7 December (Hawaii time).

On 12 February 1942, the newly commissioned super-battleship Yamato arrived at Hashirajima from Kure, and the Combined Fleet flag was transferred from Nagato to Yamato. Yamato served as the Combined Fleet flagship at this anchorage throughout 1942, including during the planning and sortie for the Battle of Midway in June 1942, when the Main Body under Yamamoto departed Hashirajima. After the Midway defeat, the surviving fleet withdrew to Hashirajima on 14 June 1942. In early 1943, super-battleship Musashi relieved Yamato as flagship.

The Mutsu Disaster

The anchorage witnessed one of the Imperial Navy's most devastating non-combat losses. On 8 June 1943, battleship Mutsu — the second Nagato-class dreadnought, armed with eight 41 cm guns — was moored at Hashirajima with her regular crew augmented by a party of flying cadets and instructors from the Tsuchiura Naval Air Group (roughly 130–150 men, depending on the source) aboard for familiarization training. Shortly after noon (12:10–12:13 in most accounts), the No. 3 turret magazine detonated catastrophically, breaking the ship in two. The 150-metre forward section capsized to starboard and sank almost immediately. The 45-metre stern section remained afloat for several hours — until the evening of 8 June or the early hours of 9 June, depending on the account — before sinking at approximately 33°58'N, 132°24'E.

Nearby vessels — battleship Fusō, destroyers Tamanami and Wakatsuki, cruisers Tatsuta and Mogami — launched immediate rescue operations, but only 353 of the 1,474 personnel aboard survived; 1,121 perished. An investigation committee chaired by Admiral Shiozawa Kōichi attributed the explosion to the No. 3 turret powder magazine but never definitively established the cause, with theories ranging from propellant decomposition to sabotage by a disgruntled crew member. The Navy suppressed all news of the disaster and dispersed survivors to prevent information leaks.

Operations Launched from Hashirajima

Throughout the war, major fleet operations staged through the anchorage:

• December 1941: Yamamoto directed Pearl Harbor operations from Nagato at anchor
• May–June 1942: The Main Body departed for the Battle of Midway
• June 1942: Returning forces regrouped at the anchorage after Midway
• 1942–1944: Successive fleet deployments for Guadalcanal, Philippine Sea, and Leyte Gulf campaigns staged or returned through Hashirajima

Decline and Abandonment

By mid-1945, intensifying Allied air attacks — particularly carrier-based air raids reaching deep into the Inland Sea — rendered the open anchorage untenable. On 19 March 1945, Task Force 58 aircraft attacked ships in the Kure–Hashirajima area. The remaining major warships were dispersed to narrow coves and inlets around Kure and nearby islands for concealment, effectively ending Hashirajima's role as the fleet anchorage. Many of these ships, including Haruna, Ise, Hyūga, and the carrier Amagi, were sunk at their dispersed moorings during the devastating Kure air raids of 24–28 July 1945.

Today, Hashira Island is a small residential community of fewer than 200 inhabitants sustained by fishing and citrus cultivation. No formal military memorial exists on the island itself, though the waters surrounding it remain the final resting place of battleship Mutsu. The nearby Mutsu Memorial Museum on Suo-Oshima and the Yamato Museum in Kure preserve artifacts and memory of the fleet that once filled this anchorage.