Among all the revered blades forged across a millennium of Japanese swordmaking, none holds a deeper mystique than the Honjo Masamune (本庄正宗). Created in the late Kamakura to early Nanbokucho period by the legendary Soshu master Goro Nyudo Masamune (五郎入道正宗), this blade was not merely a weapon of war: for more than two and a half centuries, it served as the physical emblem of the Tokugawa shogunate's right to rule Japan. Designated an official Japanese National Treasure (Kokuho) in 1939, the sword survived nearly six hundred years of feudal civil wars, castle fires, and dynastic upheavals—only to vanish without a trace in December 1945 after being handed over to a neighborhood police station in occupied Tokyo.
1. Blood and Iron at Kawanakajima (1561): How the Blade Earned Its Name
While Goro Nyudo Masamune forged the blade in Kamakura during the fourteenth century—leaving the tang unsigned (mumei), as was customary for his highest-grade works—the sword acquired its historical name two centuries later on the fog-shrouded plains of Shinano Province. During the Fourth Battle of Kawanakajima (1561), the armies of Takeda Shingen and Uesugi Kenshin clashed in one of the bloodiest engagements of the Sengoku period.
According to Edo-period military chronicles and Tokugawa family inventories, Honjo Echizen-no-kami Shigenaga (本庄越前守繁長), a ferocious commander serving under Uesugi Kenshin, was engaged in single combat by an enemy officer named Umanosuke, who wielded the Masamune blade. During the duel, Umanosuke brought the sword down with such terrifying momentum that it cleaved Honjo Shigenaga's iron battle helmet (kabuto) cleanly in two. Remarkably, Shigenaga survived the blow with only a shallow scalp wound, struck down his attacker, and claimed the sword as a battlefield trophy. Because the blade had sliced through laminated iron helmet plates without suffering a single fatal crack or roll along its cutting edge, it became known across Japan as the Honjo Masamune.
Documentary Feature: Tracing the historical provenance of the Honjo Masamune from feudal battlefields to postwar Tokyo.
2. From Fushimi Castle to the Tokugawa Shogunate Treasury
Honjo Shigenaga kept his prized trophy for more than three decades until the late 1590s, when the Honjo clan faced severe financial strain during Toyotomi Hideyoshi's compulsory construction works at Fushimi Castle. Forced to raise silver to support his retainers, Shigenaga reluctantly sold the sword for thirteen枚 (mai) of gold oban coins—a staggering sum at a time when the legendary sword connoisseur Hon'ami Koetsu appraised even top-tier masterworks at fractions of that figure.
The blade passed first to Toyotomi Hidetsugu, nephew and regent to Toyotomi Hideyoshi. Following Hidetsugu's downfall, it entered the possession of Hideyoshi himself, who later presented it to Tokugawa Ieyasu, founder of the Tokugawa shogunate. Upon establishing the Edo bakufu in 1603, Ieyasu declared the Honjo Masamune the supreme dynastic heirloom of the ruling Tokugawa main house (Shogun-ke). From Ieyasu to the second shogun Hidetada, third shogun Iemitsu, and down through the Kii branch line to Tokugawa Iemasa (the 16th head of the Tokugawa clan in the twentieth century), the sword was transmitted as the sacred regalia of shogunal authority.
3. Soshu-Den Metallurgy: What Surviving Woodblock Obrigami Reveal About the Blade
Although no modern high-resolution photograph of the Honjo Masamune exists today, its exact dimensions, curvature, and crystalline steel structures were meticulously documented in the Kyoho Meibutsu Cho (享保名物帳)—the eighteenth-century shogunal register of famous swords compiled by the Hon'ami family under Shogun Tokugawa Yoshimune—as well as in the 1939 Ministry of Education National Treasure designation dossier.
Originally forged as a long cavalry tachi, the blade had been shortened from the tang (o-suriage) to a wearable katana length of 2 shaku, 1 sun, 6 bu (approximately 65.4 cm / 25.75 inches). Its metallurgical signature epitomized the pinnacle of Masamune's Soshu-den (相州伝) innovation:
- Jihada (Surface Grain): A dynamic blend of itame-hada (wood-grain pattern) mixed with swirling mokume (burl grain), saturated with dense, sparkling ji-nie (martensitic crystal clusters visible to the naked eye) and luminous chikei (dark, glossy high-carbon lines threading through the body steel).
- Hamon (Temper Line): An undulating notare (gentle wave) pattern combined with gunome billows, executed in coarse, brilliant nie-deki rather than misty nioi. This high-temperature austenitizing quench created a wide, cloud-like transition zone packed with kinsuji ("golden threads") and inazuma ("lightning flashes").
- Boshi (Point Temper): A disordered, flame-like midare-komi temper in the kissaki with a lively return (kaeri), engineered to prevent tip snapping when impacting iron armor lamellae—precisely why the blade survived splitting Honjo Shigenaga's helmet at Kawanakajima.
4. Historical Provenance Timeline of the Honjo Masamune
| Date / Period | Custodian / Location | Documented Historical & Metallurgical Event |
|---|---|---|
| c. 1300–1330 (Late Kamakura) | Goro Nyudo Masamune (Kamakura) | Forged in Sagami Province using multi-stage laminated steel and high-temperature nie-deki differential quenching. |
| 1561 (Fourth Battle of Kawanakajima) | Honjo Shigenaga (Uesugi Clan) | Splits Shigenaga's iron kabuto helmet in combat; captured by Shigenaga and named the "Honjo Masamune." |
| c. 1592–1600 (Azuchi-Momoyama) | Toyotomi Hidetsugu → Hideyoshi → Tokugawa Ieyasu | Purchased for 13 gold oban coins; presented to Tokugawa Ieyasu and elevated to supreme heirloom of the Tokugawa shogunate. |
| 1719 (Kyoho Era) | Edo Castle Treasury (Hon'ami Registry) | Formally cataloged in the Kyoho Meibutsu Cho as an o-suriage mumei blade measuring 65.4 cm (2 shaku 1 sun 6 bu). |
| 1939 (Showa 14) | Prince Tokugawa Iemasa (Tokyo) | Designated a National Treasure (Kokuho) under Japan's National Treasures Preservation Act. |
| December 1945 – January 1946 | Mejiro Police Station (Toshima-ku, Tokyo) | Surrendered by Tokugawa Iemasa alongside 14 other family blades; logged as released to an Allied representative ("Sgt. Coldy Bimore") and vanishes. |
Archival Investigation: Full-length historical documentary examining the 1945 Allied disarmament directive and the Mejiro police logbook mystery.
5. December 1945 at Mejiro Police Station: The "Sgt. Coldy Bimore" Mystery
Following Japan's surrender in August 1945, the Supreme Commander for the Allied Powers (SCAP) issued a sweeping directive ordering the confiscation of all military and civilian weapons—including antique family swords—to prevent armed insurgency. Although SCAP officials later clarified that certified artistic and historical heirlooms were exempt from destruction, confusion reigned during the winter of 1945.
Determined to set an example of Aristocratic compliance with postwar law, Prince Tokugawa Iemasa personally instructed his household steward to deliver fourteen prized Tokugawa family swords—including the National Treasure Honjo Masamune—to the Mejiro Police Station in Tokyo in December 1945. According to the surviving Japanese police station ledger, the bundle of swords was handed over in January 1946 to a man recorded phonetically in Japanese kana as "Sgt. Coldy Bimore" (コルディ・バイモア軍曹) of the U.S. 7th Cavalry Regiment (or Foreign Liquidations Commission).
Decades of subsequent archival research by Japanese sword historians, U.S. National Archives researchers, and military genealogists revealed a startling fact: no soldier named "Coldy Bimore" ever existed on the rosters of the U.S. 7th Cavalry or Allied occupation forces. Historians widely conclude that the entry was either a garbled phonetic transcription made by a Japanese desk officer attempting to write down a spoken English phrase or name, or a deliberate alias used during the chaotic requisitioning of war trophies.
While it is theoretically possible that the blade was dumped into Tokyo Bay or melted down at the Akabane arsenal alongside thousands of mass-produced wartime shin-gunto blades, most scholars and NBTHK (Society for the Preservation of Japanese Art Swords) appraisers strongly doubt this fate. The Honjo Masamune was housed in unmistakable high-ranking shogunal mounts and storage boxes (hakogaki). Far more likely, the sword was carried back to the United States in a returning GI's duffel bag—where it may still rest today in an attic, estate closet, or regional collection, its unsigned tang masking its identity from an owner who assumes it is just another World War II souvenir.
Historical Investigation: How sword appraisers (kantei specialists) could positively identify the unsigned Honjo Masamune if it ever resurfaces.
6. Frequently Asked Questions (FAQ)
How could historians prove a found katana is the real Honjo Masamune if its tang is unsigned?
Even though the Honjo Masamune is mumei (unsigned) due to having its tang shortened (o-suriage), the Kyoho Meibutsu Cho and 1939 National Treasure registry preserve its exact blade length (65.4 cm), curvature, tang file marks (yasurime), number of peg holes (mekugi-ana), and detailed hand-drawn rubbings (oshigata) of its unique nie crystal and kinsuji patterns. In Japanese sword appraisal (kantei), an oshigata rubbing of a blade's hamon and tang is as individually unique as a human fingerprint.
Did any other Masamune National Treasure swords survive World War II?
Yes. Several authenticated masterworks by Goro Nyudo Masamune survived the war and remain preserved in Japan today as designated National Treasures, including the Kanze Masamune and Nakatsukasa Masamune (held at the Tokyo National Museum), the Fudo Masamune (owned by the Tokugawa Art Museum in Nagoya), and the Hyuga Masamune (Mitsui Memorial Museum). Studying these surviving blades allows metallurgists to examine Masamune's exact Soshu-den steel structure firsthand.
What happened to the other Tokugawa swords surrendered at Mejiro Police Station?
All fourteen swords surrendered by Prince Tokugawa Iemasa in that December 1945 bundle disappeared alongside the Honjo Masamune. However, other branches of the Tokugawa family—most notably the Owari Tokugawa branch in Nagoya, whose holdings formed the core of the Tokugawa Art Museum—successfully retained their ancestral collections after SCAP issued formal preservation permits for registered art swords in 1946.
