Also on this day:

• 1844: A 12-inch gun aboard the USS Princeton explodes as the ship is sailing on the Potomac River, killing Secretary of State Abel P. Upshur, Navy Secretary Thomas W. Gilmer and several others.
• 1849: The California gold rush begins in earnest as regular steamship service starts bringing gold-seekers to San Francisco.
• 1911: President William Howard Taft nominates William H. Lewis to be the first black assistant attorney general of the United States.
• 1917: The Associated Press reports that the United States obtained a diplomatic communication sent by German Foreign Minister Arthur Zimmermann to a German official in Mexico proposing a German alliance with Mexico and Japan should the U.S. enter World War I. (Outrage over the telegram would help propel America into the conflict.)
• 1942: The heavy cruiser USS Houston and the Australian light cruiser HMAS Perth are attacked by Japanese forces during the World War II Battle of Sunda Strait.
• 1953: Scientists James D. Watson and Francis H.C. Crick announce they have discovered the double-helix structure of DNA.
• 1993: A gun battle erupts at a religious compound near Waco, Texas, when Bureau of Alcohol, Tobacco and Firearms agents try to arrest Branch Davidian leader David Koresh on weapons charges; four agents and six Davidians are killed as a 51-day standoff begins.
• 1995: Denver International Airport opens after 16 months of delays and $3.2 billion in budget overruns.
• 1996: Britain’s Princess Diana agrees to divorce Prince Charles.
• 2009: Paul Harvey, the news commentator and talk-radio pioneer whose staccato style made him one of the nation’s most familiar voices, dies in Phoenix at age 90.
• 2009: Oakland Raiders linebacker Marquis Cooper, free-agent NFL defensive lineman Corey Smith and former South Florida player William Bleakley die when their boat overturns in rough seas off the coast of Florida.
• 2013: Benedict XVI becomes the first pope in 600 years to resign, ending an eight-year pontificate. (Benedict would be succeeded the following month by Pope Francis.)
• 2014: Delivering a blunt warning to Moscow, President Obama expresses deep concern over reported military activity inside Ukraine by Russia and warns “there will be costs” for any intervention.
• 2018: Walmart announces that it would no longer sell firearms and ammunition to people younger than 21 and would remove items resembling assault-style rifles from its website. Dick’s Sporting Goods also says it would stop selling assault-style rifles, and ban the sale of all guns to anyone under 21.
• 2018: Students and teachers returned under police guard to Marjory Stoneman Douglas High School in Parkland, Fla. as classes resume for the first time since the shooting that killed 17 people.
• 2018: Political leaders pay tribute to the Rev. Billy Graham as his casket rests in the U.S. Capitol Rotunda.