At 12:38 p.m., a blast ripped through a ninth-floor men's bathroom in the Mitsubishi Heavy Industries headquarters in Marunouchi, Tokyo's financial district. The explosion tore through elevator shafts and stairwells, collapsing ceilings and filling corridors with smoke and debris. Office workers, many on their lunch break, were trapped or crushed. Eight people died instantly or from their injuries. 378 others were wounded, making it one of the most damaging terrorist attacks in post-war Japan. The bomb, constructed from 40 kilograms of dynamite packed into two steel boxes, had been placed days earlier by activists who had infiltrated the building posing as maintenance workers.
The attack was the work of the East Asia Anti-Japan Armed Front, a small, radical left-wing group. Their target was symbolic. Mitsubishi Heavy Industries was the successor to the Mitsubishi conglomerate that built engines for Zero fighter planes and warships during Japan's imperial expansion. The group's manifesto, 'The Declaration of War Against Japanese Imperialism,' accused Mitsubishi of leading the economic re-invasion of Southeast Asia. This was not an isolated act but part of a coordinated campaign called the 'Bombing of the Imperial Army.' The same group had bombed the Mitsubishi Motor Sales office in Tokyo three months earlier, and would bomb the headquarters of the trading company Mitsui & Co. two months later.
The event is largely absent from global memory, overshadowed by contemporaneous Red Army Faction activities in Europe. Within Japan, it marked the violent peak of a specific strand of 1970s New Left activism that focused on corporate complicity in historical war crimes. The perpetrators were not seeking mass casualties but a precise, shocking strike against a corporate entity they viewed as an unrepentant engine of empire. The choice of a weekday lunch hour, however, guaranteed high civilian presence, a contradiction the group dismissed as collateral damage in a righteous war.
The investigation, which led to eight arrests by May 1975, revealed the group's meticulous planning and their ideological fixation on historical guilt. The bombing failed to ignite the popular uprising its perpetrators envisioned. Instead, it hardened public opinion against violent extremism and contributed to the decline of the New Left. Its legacy is a footnote in histories of Japanese terrorism, a stark reminder of how unresolved historical grievances can manifest in sudden, concrete violence against the architecture of economic power.