Shimonoseki Fortress (Hinoyama Battery)

The Shimonoseki Fortress (下関要塞) was a major Imperial Japanese Army coastal defense complex built to guard the Kanmon Strait (関門海峡), the narrow waterway separating Honshu and Kyushu that serves as the western gateway to the Seto Inland Sea. The fortress encompassed multiple battery positions on mountains flanking both sides of the strait — the Shimonoseki (Yamaguchi) side featuring batteries on Mount Hinoyama (火の山, 268m), Tamukeyama, and Reijusan, and the Kitakyushu (Fukuoka) side with positions from Tomino to Waburi and south to Takakurayama.

Construction began in September 1887 (Meiji 20), driven by fears of Russian and Chinese naval threats following Japan's emerging continental ambitions. The Shimonoseki Fortress Command (下関要塞司令部) was established in April 1895, and in 1899 the area was designated a fortress zone under the Fortress Zone Law. The fortress was designed to work in concert with Iki Fortress and Tsushima Fortress to control the entire Korea Strait and protect Japan's vital sea route to Korea, Manchukuo, and the Asian continent.

The Hinoyama Battery (火の山砲台) was the fortress's most prominent installation. Four separate battery positions (第一～第四砲台) were constructed on the mountaintop: Battery No. 1 and No. 2 each housed four 28cm howitzers; Battery No. 3 mounted eight 24cm cannons; and Battery No. 4 (the rampart battery) contained two 28cm howitzers, two 15cm mortars, and two 12cm cannons. These weapons commanded a devastating field of fire over the strait below.

During the 1920s and 1930s, as Japan's military posture shifted, many fortifications were re-armed and numerous anti-aircraft guns were installed. The fortress's mission evolved from purely coastal defense to include air defense of Kokura (northern Kyushu), which housed the massive Kokura Arsenal and other critical munitions plants. A Type 14 10-cm anti-aircraft gun was among the weapons emplaced at Hinoyama during this period.

In the final months of WWII, the Kanmon Strait became the primary target of Operation Starvation (飢餓作戦), the devastating American aerial mining campaign. Beginning on the night of March 27–28, 1945, B-29 Superfortresses of the 313th Bombardment Wing, XXI Bomber Command, flying from the Mariana Islands, began dropping thousands of naval mines into the strait and surrounding waters. The campaign's Phase 1 (March 27 – April 12) focused on the Shimonoseki Straits and the western Inland Sea: 2,030 mines were laid, and after the first drop the strait was closed to traffic for two days while it was swept. Daily traffic through the strait fell from about 40 ships in March to only two to four by the end of May. Over the course of the operation, 1,529 B-29 sorties laid 12,135 mines that sank or damaged 670 ships totaling over 1.25 million tons — more tonnage than all other attacks combined in the war's final six months. The mine blockade effectively strangled Japan's ability to transport food, raw materials, and military supplies through its most critical domestic waterway.

Today, only the remains of Battery No. 3 and Battery No. 4 survive at Hinoyama. Battery No. 1 was destroyed during construction of the Hinoyama Ropeway station, and Battery No. 2 was demolished to build an observation deck. Battery No. 3's gun positions now serve as a bus turnaround area, with its underground shelter sections converted to rest areas. Battery No. 4 lost sections to radio tower construction. Nevertheless, five underground chambers from the battery complex remain in nearly original condition, and visitors can walk through them. A 46cm main gun shell from the battleship Yamato is displayed outdoors at the park. The site was designated a JSCE (Japan Society of Civil Engineers) Selected Civil Engineering Heritage (土木学会選奨土木遺産). The mountaintop is accessible by car via Hinoyama Parkway (the Hinoyama Ropeway ceased operation in November 2024, with a replacement gondola planned), and the battery ruins can be explored on foot within Hinoyama Park.