On September 15, 1916, during the Battle of the Somme, British forces introduced a weapon that would permanently change land warfare: the tank. Used during the Battle of Flers-Courcelette in northern France, the early machines were slow, mechanically unreliable and extraordinarily cumbersome by later standards. Of the roughly 49 tanks allocated for the attack, only a portion actually reached the battlefield and went into action, with breakdowns and difficult terrain sidelining many of them. Those that did advance demonstrated something important, however: armored vehicles could cross trenches, crush barbed wire and help infantry penetrate fortified positions. Some British troops advanced significantly during the attack, although the tanks were nowhere near numerous or dependable enough to produce the decisive breakthrough commanders hoped for. Field Marshal Sir Douglas Haig nevertheless recognized their potential and pressed for substantially greater production.

The tanks appeared against the background of one of the bloodiest campaigns of the First World War. The Somme offensive had begun on July 1, 1916, following an enormous week-long Allied bombardment intended to destroy German defenses. British commanders expected the shelling to have devastated enemy positions, but many German soldiers had survived in deep dugouts, while machine-gun positions and other defenses remained operational. When British infantry advanced across no-man's-land, they encountered devastating fire. The British Army suffered approximately 57,000 casualties on the first day, including more than 19,000 men killed, making July 1, 1916, the bloodiest single day in its history. Fighting continued through the summer as British and French forces attempted to grind their way forward against determined German resistance, with enormous losses suffered for relatively small territorial gains.

Neither the appearance of the tanks in September nor subsequent Allied attacks produced the long-awaited breakthrough. Autumn rain eventually transformed the already shattered battlefield into deep mud, making movement increasingly difficult, and the Somme offensive ended in November after more than four months of fighting. Allied forces had advanced only several miles at their deepest penetration, while British, French and German armies together suffered well over a million casualties. The offensive did place enormous pressure on the German Army and helped relieve pressure on French forces fighting at Verdun, but its human cost ensured that the Somme became an enduring symbol of the slaughter of trench warfare. The primitive tanks of Flers-Courcelette did not win the battle, but their appearance on September 15 offered an early glimpse of a technology that would develop rapidly and fundamentally alter warfare in the decades ahead.

On September 15, 1950, U.S. Marines began an amphibious assault at Inchon on Korea's west coast, launching one of the most daring operations of the Korean War. General Douglas MacArthur had strongly supported the plan despite serious concerns about Inchon's narrow channels, extreme tides, mudflats and fortified approaches, all of which made an amphibious landing unusually hazardous. The gamble succeeded. U.N. forces overcame North Korean resistance, secured Inchon and advanced toward nearby Seoul. Coming while other U.N. and South Korean forces were fighting from the Pusan Perimeter in southeastern Korea, the landing threatened North Korean supply and communication lines and forced an army that had spent months advancing southward to contend with an attack deep behind its positions. Seoul was subsequently recaptured, and North Korean forces suffered severe losses as they retreated north.

The dramatic reversal came less than three months after the war began. On June 25, 1950, North Korean forces crossed the 38th parallel and invaded South Korea, quickly overwhelming much of the South Korean resistance and capturing Seoul. President Harry S. Truman committed American forces to the defense of South Korea under a United Nations command, with MacArthur appointed commander of the U.N. forces. After Inchon and the breakout from the Pusan Perimeter, U.N. troops drove northward beyond the 38th parallel. The course of the war changed again when large numbers of Chinese troops entered the fighting in late 1950, forcing U.N. forces south. MacArthur later clashed publicly with the Truman administration over how the war should be conducted and was relieved of his command in April 1951.

By the middle of 1951, the front had stabilized generally around the 38th parallel, and the conflict became another grinding war of fortified positions and limited advances while lengthy armistice negotiations proceeded. Fighting finally stopped with the signing of the Korean Armistice Agreement on July 27, 1953, establishing a military demarcation line and the Korean Demilitarized Zone rather than a permanent peace treaty. The Korean Peninsula consequently remained divided between North and South. The war killed and wounded enormous numbers of military personnel and civilians on all sides, while the precise casualty totals remain disputed among historical sources. The Inchon landing nevertheless stands as a pivotal moment in the conflict: an exceptionally risky amphibious operation that transformed a desperate defensive campaign into a rapid U.N. counteroffensive and demonstrated just how dramatically the direction of a war could change in a matter of weeks.

On September 15, 1962, Frankie Valli and the Four Seasons reached No. 1 on the Billboard Hot 100 with “Sherry,” beginning an extraordinary run of hit records that would make the group one of the defining American pop acts of the 1960s. Success had hardly arrived overnight. Valli, born Francesco Castelluccio, had spent years pursuing a music career before the classic Four Seasons lineup emerged. The group evolved through several earlier configurations and had performed as the Four Lovers before adopting the Four Seasons name in 1961, reportedly taking their new identity from a bowling establishment where they had unsuccessfully auditioned. Apparently, failing to get the gig was considerably more useful than getting it.

The breakthrough song came from keyboard player Bob Gaudio, who wrote “Sherry” shortly before a rehearsal. Gaudio later recalled composing it extremely quickly and then driving to meet the group while repeatedly singing the unfinished song to himself so he wouldn't forget it. He initially regarded the lyrics as temporary, but the other members liked what they heard and little needed changing. Released in August 1962, the record raced up the charts, propelled by Valli's unmistakable falsetto, and reached the top only weeks later. It was no isolated success: “Big Girls Don't Cry” followed it to No. 1 later that year, and “Walk Like a Man” gave the Four Seasons another chart-topper in 1963.

The hits continued throughout the decade, with songs including “Candy Girl,” “Dawn (Go Away),” “Ronnie,” “Save It for Me,” “Let's Hang On!” and “Working My Way Back to You,” while “Rag Doll” became another No. 1 single in 1964. The arrival of the Beatles and the British Invasion swept many established American acts aside, but the Four Seasons remained remarkably successful. More than a decade after “Sherry” first put them on top, the group enjoyed another major resurgence with “Who Loves You” and then returned to No. 1 in 1976 with “December, 1963 (Oh, What a Night).” What began with a quickly written song, an unforgettable falsetto and the borrowed name of a bowling alley became a pop career lasting generations—and “Sherry” was the record that opened the door.

On September 15, 1971, a small group of activists left Vancouver aboard an aging fishing vessel called the Phyllis Cormack, which they used for the voyage under the name Greenpeace. Their destination was Amchitka Island in Alaska's Aleutian chain, where the United States planned to conduct an underground nuclear weapons test. Opposition to the test had helped inspire the Vancouver-based Don't Make a Wave Committee, whose members worried about the environmental consequences of detonating a powerful nuclear device in a geologically active region. Drawing inspiration from earlier protests in which activists sailed toward nuclear testing areas, the group hoped that placing themselves near Amchitka—and attracting extensive news coverage while doing so—might persuade the United States to cancel the explosion. The expedition did not reach its intended destination, but its unusual combination of environmental protest, direct action and publicity attracted considerable attention.

The test went ahead despite the campaign. On November 6, 1971, the United States detonated Cannikin, a nuclear device buried roughly 6,000 feet beneath Amchitka. With a yield of less than five megatons, it was the largest underground nuclear test ever conducted by the United States. The explosion produced substantial ground movement and raised continuing concerns about the environmental effects of nuclear testing on the remote island. Cannikin was the third and final underground nuclear test conducted at Amchitka; the United States carried out no further nuclear explosions there.

Although the activists failed in their immediate objective of preventing Cannikin, their voyage proved far more significant than the fate of a single protest. The name Greenpeace, combining concern for the environment with opposition to nuclear weapons, became attached to the movement itself, and the organization subsequently expanded its campaigns to include nuclear testing, whaling, pollution, conservation and other environmental issues around the world. What began with a handful of campaigners aboard an old fishing boat sailing toward Alaska therefore became the origin story of one of the world's best-known environmental organizations. They didn't stop the bomb—but the voyage launched something that traveled considerably farther than the boat ever did.

On September 15, 1978, Muhammad Ali defeated Leon Spinks at the Louisiana Superdome in New Orleans, becoming the first boxer to win the world heavyweight championship three times. Spinks had stunned Ali seven months earlier in Las Vegas, taking the title by split decision in only his eighth professional fight. Their rematch attracted an enormous crowd and television audience, but this time Ali controlled the contest and won a unanimous decision after 15 rounds. It was another remarkable chapter in a career that had begun under the name Cassius Marcellus Clay Jr. Born in Louisville, Kentucky, in 1942, Ali won light-heavyweight gold at the 1960 Rome Olympics before turning professional. In 1964, he shocked heavily favored Sonny Liston to become heavyweight champion and soon became almost as famous for his confidence, wit and verbal sparring as for his extraordinary speed and skill inside the ring.

Ali's career was interrupted during the Vietnam War when he refused induction into the U.S. Army on religious grounds. He was convicted in 1967 of refusing induction, stripped of his boxing licenses and titles, and kept out of the ring during several prime years of his career while his case moved through the courts. He returned to boxing in 1970, and in 1971 suffered his first professional defeat when Joe Frazier beat him in their celebrated "Fight of the Century." The U.S. Supreme Court unanimously reversed Ali's conviction later that year. Ali defeated Frazier in a 1974 rematch and then traveled to Kinshasa, Zaire, where he faced the fearsome and heavily favored George Foreman in the "Rumble in the Jungle." Using the strategy that became famous as the rope-a-dope, Ali allowed Foreman to exhaust himself before knocking him out in the eighth round and reclaiming the heavyweight championship.

After regaining the title from Spinks in 1978, Ali announced his retirement the following year, but the retirement proved temporary. He returned in 1980 to challenge heavyweight champion Larry Holmes and was stopped after the tenth round when his corner ended the fight before the eleventh began. Ali fought once more, losing a decision to Trevor Berbick in December 1981, and retired permanently with a professional record of 56 victories and five defeats, including 37 wins by knockout. He was diagnosed with Parkinson's syndrome in the 1980s and subsequently became an internationally recognized humanitarian and public figure, famously lighting the Olympic cauldron at the 1996 Atlanta Games before his death in 2016. Yet September 15, 1978, remains one of the defining dates of his boxing career: seven months after losing his championship to Spinks, Ali stepped into the ring, took it back and accomplished something no heavyweight champion before him had managed—winning the title for a third time.