This week, 150 years ago, New Orleans witnessed one of the few sights never before seen in that old and unpredictable city: a hostile squadron of a dozen warships right there at the downtown wharfs. The river was unusually high, and hundreds of federal cannons leveled at the city were above street level. The U.S. fleet scattered the Confederate defenses and sent the city into a panic. Citizens set supplies ablaze, threw cotton bales into the water.

At the helm of the USS Harford, in charge of the Union squadron, was a sturdy commander named David Glasgow Farragut.

Even in panic, the city was defiant. Protected from massive flooding by dirt levees, New Orleans would have been rather easy to destroy. Flag Officer Farragut shrugged and sailed upriver, securing a couple more rebel forts before returning to the city, where reality was beginning to sink in. On April 29, 250 of Farragut’s marines entered the city on foot, leading the way for Gen. Butler’s occupying force of 5,000, waiting in troop ships. The Confederacy was only one year old, but thanks to Farragut’s boldness, its largest city, and the mouth of its largest river, was permanently under Union occupation....