A bomb exploded during San Francisco’s Preparedness Day parade, killing ten people and injuring approximately forty others. The attack occurred near the intersection of Market and Steuart Streets, close to the Ferry Building, as thousands of marchers and spectators participated in one of the largest public demonstrations in the city’s history. The bombing became historically significant because it joined the national debate over American military preparedness with San Francisco’s bitter conflict between organized labor and business interests. Its aftermath also produced one of the most disputed criminal prosecutions of the twentieth century.
The parade supported the Preparedness Movement, a national campaign that sought to expand the United States Army and Navy while the First World War continued in Europe. Former President Theodore Roosevelt, military officials, business leaders, and other advocates argued that the country lacked sufficient forces to defend itself. President Woodrow Wilson initially resisted large military increases but later supported greater preparedness as German submarine warfare and other international crises threatened American neutrality. Preparedness parades took place throughout the nation during 1916, including major demonstrations in New York and Washington, D.C.
San Francisco’s parade reflected these national concerns but also exposed local political divisions. The city’s Chamber of Commerce and leading employers strongly supported preparedness. Many labor activists, socialists, anarchists, and antiwar citizens opposed the campaign because they associated military expansion with conscription, industrial profits, and possible American entry into the European war. Organized labor also had a contentious relationship with San Francisco employers, who had attempted to weaken union influence and promote open-shop employment.
Shortly before the parade, newspapers received an unsigned warning that threatened violence against the event. Municipal authorities allowed the procession to proceed. At approximately 2:06 p.m., a suitcase containing explosives detonated beside a building at Market and Steuart Streets. The device reportedly contained metal fragments intended to increase its destructive force. Six victims died immediately, and four others later died from their injuries. The explosion interrupted the parade, but organizers resumed the procession after authorities removed the dead and wounded.
Police and prosecutors soon concentrated their investigation on radical labor activists. Authorities arrested Thomas J. Mooney, Warren K. Billings, Rena Mooney, Israel Weinberg, and Edward Nolan. Thomas Mooney was a socialist labor organizer who had participated in strikes and militant labor campaigns. Billings was another labor activist with a previous conviction involving explosives. Their political records made them prominent suspects, although their reputations did not establish responsibility for the bombing.
Separate juries convicted Billings and Mooney of murder. Billings received a life sentence, while Mooney received a death sentence. The prosecution relied heavily upon eyewitness testimony that later became discredited. John McDonald, a principal witness, eventually repudiated his testimony. Questions also arose concerning Frank Oxman, who claimed that he had observed Mooney and Billings near the bombing site. Evidence indicated that Oxman had attempted to secure supporting testimony from another person who had not witnessed the events.
Photographs provided additional grounds for challenging the prosecution. Images taken from the roof of the Eilers Building appeared to show Thomas and Rena Mooney at a location distant from Market and Steuart Streets shortly before the explosion. These photographs became central evidence for the defense campaign. The controversy attracted journalists, labor organizations, civil libertarians, and international observers who argued that political hostility had influenced the investigation and trials.
President Wilson intervened because labor unrest surrounding the case threatened wartime industrial production. His administration’s Mediation Commission examined the controversy and reported serious doubts about the fairness of Mooney’s conviction. Wilson urged California officials to reconsider the sentence. Governor William D. Stephens commuted Mooney’s death sentence to life imprisonment in 1918, but he did not grant a pardon.
The Mooney-Billings case developed into an international campaign lasting more than two decades. Supporters organized defense committees, demonstrations, publications, and legal appeals. The campaign linked their imprisonment to broader concerns about prosecutorial misconduct, unreliable eyewitness testimony, political prejudice, and the treatment of unpopular defendants. The case remained prominent during the First Red Scare, when federal and local authorities prosecuted radicals and restricted dissent after the United States entered the First World War.
California Governor Culbert L. Olson granted Mooney an unconditional pardon on January 7, 1939. Billings was released later that year after Governor Olson commuted his sentence. Governor Edmund G. Brown pardoned Billings in 1961. No other person was convicted of carrying out the bombing, and the identity of the person or group responsible remains undetermined.
The Preparedness Day bombing marked a deadly episode of domestic political violence during a period of war anxiety, labor conflict, and ideological division. Its lasting significance rests equally in the attack and in the failed administration of justice that followed it. The bombing killed innocent spectators, intensified suspicion of political radicals, and produced convictions that collapsed under evidence of unreliable and false testimony. The case became a lasting warning that fear, political pressure, and hostility toward defendants can compromise criminal investigations and judicial proceedings.
References / More Knowledge:
California State Library. “Governors of California: Culbert L. Olson.” https://governors.library.ca.gov/29-olson.html
Johnson, Jeffrey A. The 1916 Preparedness Day Bombing: Anarchy and Terrorism in Progressive Era America. New York: Routledge, 2017. https://www.routledge.com/The-1916-Preparedness-Day-Bombing-Anarchy-and-Terrorism-in-Progressive-Era-America/Johnson/p/book/9781138672831
Library of Congress. “Photo Shows General View of the Preparedness Day Parade at San Francisco in 1916.” https://www.loc.gov/pictures/item/2016651585/
Library of Congress. “Warren K. Billings Papers.” https://findingaids.loc.gov/repositories/19/resources/4209
National Registry of Exonerations. “Thomas J. Mooney.” https://www.law.umich.edu/special/exoneration/Pages/casedetail.aspx?caseid=4528
Online Archive of California. “Thomas J. Mooney Papers, 1887–1949.” https://oac.cdlib.org/findaid/ark:/13030/kt0f59r8q2/
San Francisco Chronicle. “Centennial of 1916 S.F. Bombing That Led to Infamous Convictions.” https://www.sfchronicle.com/bayarea/article/Centennial-of-1916-SF-bombing-that-led-to-8381615.php
TIME. “The Bomb That Rocked San Francisco 100 Years Ago.” https://time.com/4411324/san-francisco-1916-bombing-preparedness-day-parade-anniversary-centennial/