Snoopy, who first appeared in the Peanuts comic strip in 1950, has been everywhere at this point: summer camp, college, the desert to visit his hapless brother, Spike. He has been to the airfields of the First World War in his unceasing fight with the Red Baron, and even to the moon with the crew of Apollo 10.

He also went to Normandy, France, in a national call for remembrance and unity. And there, he became part of D-Day’s pop-culture legacy, one that has shaped Americans’ understanding of the invasion, and indeed, the Second World War, for decades.

This week marks the 75th anniversary of D-Day, when the Allies invaded Europe. Code-named Operation Overlord, this amphibious landing marked the official opening of Joseph Stalin’s long-requested “second front” in the European war against Nazi Germany. Three million Allied troops, supported by more than 10,000 aircraft and nearly 7,000 naval ships, participated in an assault on the Nazi-controlled beachheads. By the end of the operation later that month, both sides had experienced about 425,000 casualties.

This offensive marked the beginning of the liberation of France and the eventual Allied victory. It also profoundly influenced the way that we remember the war in popular culture. That is in part because D-Day was a highly visible moment in the Allied war effort. The US military heavily documented the event, sending in some 400 photographers and cameramen with the troops.

But it is also because of the way postwar media productions highlighted the event. The 1962 film The Longest Day, starring John Wayne, exemplified this phenomenon. The movie, which commemorated the 25th anniversary of D-Day, drew critical and popular acclaim, winning two Academy Awards and becoming a box-office hit. It focused largely on the soldiers’ experiences, attempting to show the battle from both the Allied and German sides.

By D-Day’s 50th anniversary in the mid-1990s, American popular culture teemed with documentaries, ceremonies, books and other fanfare to commemorate the events of the Second World War. In some ways, 1990s pop culture was dominated by reverence for the Second World War, whether in bestsellers such as Stephen Ambrose’s 1994 book D-Day or Hollywood blockbusters such as Steven Spielberg’s 1998 film Saving Private Ryan.

Still, there was a persistent sense in the country that the turmoil of the five intervening decades, not to mention the racial and partisan strife of the 1990s, had led Americans to overlook those whom Tom Brokaw called our “greatest generation”.

Charles Schulz, creator of Charlie Brown, Snoopy, Lucy van Pelt and the other Peanuts characters, entered the 1990s as an elder statesman in American popular culture. In one way or another, Schulz’s work had been at the centre of pop culture for more than 40 years. Some critics felt it was time for him to move on, that Schulz had nothing left to say at that point, and wrote as much in leading national outlets. But Schulz still believed he had more to offer. Foremost, he wanted to call Americans at the end of the 20th century to remembrance.

On June 6, 1993, Schulz drew a comic strip that had little visual relationship to anything that had previously appeared in Peanuts. In three grim panels, the cartoonist depicted the eerie silence at the outset of the D-Day invasion. One panel looked atop the beachhead at the Nazi bunkers, where hidden soldiers were ready to fire down on the Allied troops below. The next panel surveyed a Higgins boat carrying a crew of faceless soldiers to a murky landing site. And the final panel revealed Snoopy dressed as a GI crawling up on to the beach at low tide. The lone words on the page read: “June 6, 1944, To Remember.”

Schulz was no stranger to the solemn. In fact, he had built his reputation on his ability to blend humour with the bittersweet frustrations of life. Neither was he a stranger to war. Schulz had been drafted shortly after graduating from high school and spent three years in the military, serving as an army staff sergeant and leader of a machinegun squadron in Germany during the Second World War.

This background influenced his later art: some of his earliest attempts at comic art in the postwar years were based on the soldiers’ experiences. One of his longest-running tributes in Peanuts was regularly addressed to Stars and Stripes cartoonist Bill Mauldin, whose Willie and Joe cartoon had been popular among soldiers during the war. And one of the strip’s most iconic themes had been Snoopy’s relentless First World War-era dogfights with the Red Baron during the tumultuous days of the 1960s and the Vietnam War.

This D-Day comic strip, however, was different. Snoopy’s war had become increasingly extravagant over the years, drawing readers into the character’s vivid imagination. But never before had Schulz used his strip to illustrate such a weighty scene in such realistic detail.

Schulz got at least one reader’s attention. Dorothy Sand, from Chicago, wrote to the Chicago Tribune on June 12, 1993, accusing them of having their “priorities mixed up”. Instead of carrying photographs of the Japanese royal wedding that summer, Sand thought that Schulz’s strip “should have been Page 1 news”.

The next year, the 50th anniversary of D-Day, Schulz made sure that as many people as possible would see his tribute, whether it was on the front page or not. In a weeklong series, Snoopy acted out various events in Operation Overlord, as the neighbourhood children called Charlie Brown to complain about the mess the dog was making in their yards.

In the subsequent years, Schulz’s tributes became more formalised, simply showing Snoopy wading ashore at the rugged beach over the invocation “To Remember”. Despite the simplicity, it was a meaningful statement to some readers. Robert A. Nottke, a Second World War veteran, wrote to the Chicago Tribune to complain that he could not find a single reference to D-Day on June 6, 1996, “with one exception”. It was “Snoopy, our beloved beagle, bravely dog-paddling towards Normandy Beach”.

Nottke, and undoubtedly other readers, “felt affronted by [the] oversight”. For those who had served and their loved ones, who felt as if the sacrifices of that day and month had been forgotten over time, Schulz’s strip was salve on the wound.

The D-Day tribute in 1998 came on Memorial Day weekend when Schulz delivered something highly unusual in Peanuts: an adaptation of a famous historical photograph. In the colourised photograph, General Dwight D. Eisenhower addressed the troops of the 82nd Airborne before they set out for France. Snoopy, dressed in battle gear, joined the soldiers, gazing up at Eisenhower as he spoke.

Schulz later revealed that he received more fan response to that tribute than any other comic strip he had drawn. Some of the soldiers in the photo even reached out to thank Schulz for his work. Through Snoopy, Schulz was connecting Americans with his call to remembrance and national unity. “We have a tendency to forget very quickly the sacrifices that others have made for us,” the cartoonist told one reporter. He wanted to do his part to combat that tendency.

Because of his continuing commitment to memorialise the invasion, Schulz was selected to chair a committee to build the National D-Day Memorial in Bedford, Virginia. He personally donated $1 million to the effort. Unfortunately, he did not live to see the memorial’s completion, nor that of the National World War II Memorial. He did not see the D-Day Memorial face budget overages or fraud charges or heated debates about interpreting the monument. He did not see a generation’s reassessment of the legacy of the Second World War and its shortcomings. But Schulz, like the Allied soldiers, had helped to make such cultural conflicts possible.

He was right to do so. In our own moment of turmoil and challenge, let us recall: we have much to remember, much to contemplate and much to live up to. Even more, we must honour the sacrifices of the past by pushing freedom and equality beyond what the soldiers landing on France’s beaches 75 years ago even dreamt possible.

• Blake Scott Ball is assistant professor of history at Huntingdon College and author of the forthcoming book Charlie Brown’s America: The Popular Politics of Peanuts