Yosami Radio Transmitting Station

The Yosami Radio Transmitting Station (依佐美送信所) was constructed in 1929 in Yosami Village (依佐美村, now part of Kariya City), Aichi Prefecture, as a very large VLF (Very Low Frequency, 超長波) radio transmitting facility for intercontinental wireless communications. The station was built by the government-backed Japan Wireless Telegraph Company (日本無線電信株式会社), with the Ministry of Communications operating it, and with German technical cooperation — the high-frequency generators and core transmitting equipment were manufactured by Telefunken in Germany, while the eight 250-meter steel towers and antenna wires were designed and built in Japan. At completion, the 250-meter towers were the tallest structures in Japan.

The station's antenna system consisted of wires strung between the eight towers in a massive array, transmitting at 17.442 kHz with an output power of 500 kW — making it one of the most powerful VLF transmitters in the world. On April 15, 1929, the station began transmitting to Warsaw, establishing Japan's first direct wireless telecommunications link with Europe; the opening ceremony was held on April 18. This achievement dramatically improved Japan's diplomatic and commercial communications.

From around 1941, the long-wave equipment of the Yosami Radio Transmitting Station was used by the Imperial Japanese Navy (日本海軍) for submarine communications. VLF radio waves have the unique property of penetrating seawater to a certain depth, making them essential for communicating with submerged submarines. On December 2, 1941, the coded attack order "ニイタカヤマノボレ一二〇八" (Niitakayama Nobore 1208 — "Climb Mount Niitaka, 1208") was issued from the flagship Nagato at Hashirajima anchorage. The order was relayed through Tokyo and transmitted onward via multiple stations. Historical research indicates that Funabashi Transmitting Station handled the short and medium wave transmission, while Yosami transmitted the order via VLF (17.44 kHz) specifically to reach submarines. A submarine's daily journal documented receiving a VLF message at 17.44 kHz from Tokyo's station on that date. The role of the previously suspected Hario station has been largely discounted due to lack of evidence.

Following Japan's surrender in August 1945, the Allied General Headquarters (GHQ) initially ordered the station demolished in 1947. However, given the strategic value of the VLF facility for Cold War submarine communications, the station was instead taken over for US Navy use in 1950 and resumed transmitting in July 1952. It served the US Navy for 41 years as a key Pacific submarine communications hub, transmitting to American submarines across the western Pacific. Operations ceased in 1993, and the station was returned to Japan in 1994.

The eight iconic 250-meter steel towers — which had served as the landmark of Kariya for nearly seven decades — were demolished in 1997. The remaining station buildings were torn down in 2006. Part of the site — the former staff housing area — was redeveloped as Floral Garden Yosami (フローラルガーデンよさみ), a public park and botanical garden.

In April 2007, the Yosami Radio Transmitting Station Memorial Museum (依佐美送信所記念館) opened within the park, preserving the original Telefunken high-frequency generator, portions of the transmitting equipment, and the base section of one of the steel towers, which was relocated and rebuilt at the museum site. The high-frequency generator was designated a Heritage of Mechanical Engineering (機械遺産) by the Japan Society of Mechanical Engineers in 2007, and the complete transmitting equipment set was registered as an Essential Historical Material for Science and Technology (未来技術遺産) by the National Museum of Nature and Science in 2008. On May 19, 2009, the IEEE (Institute of Electrical and Electronics Engineers) recognized the Yosami Radio Transmitting Station with an IEEE Milestone award, commemorating it as the birthplace of the first wireless communications between Japan and Europe.