As World War II continued to rage on January 7, 1943, Theodor Geisel reported for duty. Dressed in a size 40-long captain’s uniform, the U.S. Army’s newest volunteer boarded a train for California, leaving behind his New York apartment as well as his budding career writing and illustrating children’s books under his distinctive pseudonym—Dr. Seuss.

Three years earlier, Geisel had been at work on his fourth children’s book, “Horton Hatches the Egg,” when a news flash on the radio announced that Paris had fallen to the Nazis. Having dabbled in political cartoons during the 1930s, Geisel felt compelled to put his projects for young readers aside and brandish his pen to fire satirical shots at Adolf Hitler and American isolationists such as aviation pioneer Charles Lindbergh who wanted to keep the country out of the war in Europe. “While Paris was being occupied by the clanking tanks of the Nazis and I was listening on my radio, I found that I could no longer keep my mind on drawing pictures of Horton The Elephant. I found myself drawing pictures of Lindbergh The Ostrich,” he said.

In 1941 and 1942, Geisel drew over 400 editorial cartoons for the left-leaning tabloid newspaper PM. Although the cartoons sport his distinctive style and a fanciful menagerie of creatures, the subject matter is quite foreign, in more ways than one, to Dr. Seuss readers. One cartoon depicts a “Lindbergh Quarter” with an ostrich sticking its head in the ground in place of an American eagle. Another showed Lindbergh patting the head of a swastika-covered sea serpent that sported Hitler’s trademark mustache.

When Geisel heard the news of the bombing of Pearl Harbor, he put down his copy of the Sunday New York Times and went to his drawing board to sketch a Seussian bird labeled “ISOLATIONISM” being blasted high into the sky by an explosion. “He never knew what hit him,” read the caption. With the United States now at war with Japan, Geisel’s cartoons increasingly trafficked in racial stereotypes. He portrayed Japanese leaders as narrow-eyed, buck-toothed caricatures, and one xenophobic cartoon portrays Japanese-Americans on the West Coast waiting in a long line for blocks of dynamite as well as “the signal from home.”

The American government enlisted the illustrator in the war effort by having him draw cartoons that urged the conservation of resources and the purchase of savings bonds and stamps to raise money for the war effort. Wishing to do more to back the war that he had lobbied for, the 38-year-old Geisel joined the U.S. Army and was deployed to the Fox studios in Hollywood—dubbed “Fort Fox”—to serve with some of the country’s top filmmakers, screenwriters, animators and journalists in Oscar-winning director Frank Capra’s Signal Corps unit.

Geisel worked to enliven the typical training manuals with his imaginative characters, such as an anthropomorphized malaria-carrying mosquito named Ann who eschewed whiskey and gin for the blood of soldiers and the “squander bug” who feasted on money that could have been better spent on war bonds.

He also worked alongside famed Warner Bros. animation directors Chuck Jones and Friz Freleng in creating cartoon shorts featuring Private Snafu—a bald, bumbling GI with the looks of Elmer Fudd and the voice of Bugs Bunny (Mel Blanc supplied the voices of both characters). In nearly 30 episodes, the misadventures of the inept soldier both entertained and educated servicemen by demonstrating the pitfalls of doing things exactly as they shouldn’t be done—such as disobeying orders, evading censors and leaking classified information.

Geisel wrote rhyme-studded scripts and contributed to storyboards of the cartoon, which was considerably more risqué than even the looniest of Looney Tunes (although the acronym that inspired the character’s name was sanitized to “Situation normal all FOULED up”). Since “Private Snafu” was released to only a military audience, it was not subject to the censors upholding the Motion Picture Production Code and could feature mild profanity, occasional off-color jokes and double entendres such as the hazards of “booby traps” posed by buxom spies. One episode even depicted a mosquito named “Malaria Mike” taking aim at Private Snafu’s bare bottom as he bathed in a river.

After being promoted to major in March 1944, Geisel shifted his focus to live-action documentaries, such as “Your Job in Germany,” which explained to American soldiers what their mission would be after an eventual Nazi surrender. The propaganda film came with the ominous message that Germans could not be trusted: “The Nazi Party may be gone, but Nazi thinking, Nazi training and Nazi trickery remain. The German lust for conquest is not dead.” When Geisel traveled to Europe to show high-ranking generals the top-secret film, he suddenly found himself trapped for three days behind German lines at the onset of the Battle of the Bulge before he could be rescued. While General Dwight Eisenhower and others gave their approval to the documentary, the only poor review came from General George Patton, who panned it with a one-word profanity before walking out of the screening.

Another film for which Geisel wrote a script, “Know Your Enemy—Japan,” was released on the same day the atomic bomb fell on Nagasaki, and General Douglas MacArthur ordered it quickly withdrawn. Another 18-minute film that Geisel produced following Capra’s discharge, “Our Job in Japan,” met a similar fate as MacArthur prevented its release following its completion. All was not lost, however, as Geisel and his wife, Helen, used the film as the basis for their screenplay for the 1947 documentary “Design for Death,” which earned an Academy Award.

After a three-year stint in the military, Geisel finally returned to civilian life, having received the Legion of Merit award for “exceptionally meritorious service in planning and producing films, particularly those utilizing animated cartoons, for training, informing, and enhancing the morale of the troops.” And with the publication of “McElligot’s Pool” in 1947, Dr. Seuss finally returned from the war effort as well.