For the third time in two years, Channing Tatum (“G.I. Joe: The Rise of Cobra”) has chosen to accessorize his chiseled abs with — you guessed it — a military uniform and a troubled past. For the first time, however, the hip-hop-dancing, gun-blasting actor miraculously forgoes his usually stilted delivery in favor of some genuine emotion both onscreen and off.

In “Dear John,” based on the tear-jerking Nicholas Sparks novel of the same name, Tatum plays John Tyree, a tough Special Forces soldier on leave in scenic South Carolina. There, he meets altruistic Savannah (Amanda Seyfried, “Jennifer’s Body”) and the two embark on a whirlwind romance until John returns overseas to finish up his assignment. Although he tearfully vows to come back to her at the end of his 12-month deployment, the unexpected tragedy of 9/11 throws an all-too-real wrench into the wheels of that promise, and the decision it triggers sets off a series of heartbreaking events.

“We knew we were going to be digging our fingers down into it,” said Tatum of the story’s emotional depth in a conference call with the Wheel. “In ‘G.I. Joe,’ there’s not a lot of emotion. It’s a lot of explosions and stuff and it was a great change of pace to get to sit on a beach with somebody and actually look them in the eye and have a real conversation.”

Those sentimental conversations, however, play an unfortunately large role in the film. While John is deployed, he and Savannah struggle to keep their fledgling romance alive — and the audience interested — with a series of letters that, while touching, do little to add depth to their relationship.

Similarly, while Tatum undoubtedly delivers the most heartfelt performance of his career thus far, his emotional breakdowns simply do not compare to Ryan Gosling’s rain-sodden exclamation, “I wrote you every day for a year.”

Given that “Dear John” comes from the same literary mind that set the bar for hopeless romances everywhere with “The Notebook,” there is, predictably, an excessive amount of sap running through this sometimes wooden love story. The film juggles everything from autism to war, and the end result is a story that sags under the weight of its own emotional baggage.

Despite the film’s overabundance of sentimentality, a particularly poignant subplot — and the film’s most satisfying storyline overall — arises between John and his reclusive father (Richard Jenkins, “Burn After Reading”).

Jenkins beautifully captures his character’s social anxiety with subtle, emotive gestures and brings some much-needed authenticity to an otherwise superficial script. The actor also offered support for the less-experienced Tatum while filming a challenging hospital scene.

“I owe that entire scene to him because it’s a very emotional scene,” Channing said. “I haven’t really had a lot of experiences with those in my career. He was just so there for me.”

Tatum, who worked closely with writers and producers for nearly four years, insisted that “Dear John” focuses on the novel’s romantic plotline rather than its post-9/11 backdrop.

“We didn’t want to see John with a weapon on all the time, slogging through really dangerous places,” Tatum said. “Yes, that is what happened in the book and in the movie, but we really just wanted it to be about two kids falling in love.”

Although “Dear John” follows the usual boy-meets-girl formula for its first half-hour, the film’s ending, although not particularly surprising, is certainly unexpected in a Hollywood romance.

“We had talked a lot about the end of the movie and how do it. The book is a little sad at the end, but they leave it open-ended in a way,” Tatum said. “We didn’t change the book. We added another page.”

Although the film offers its conclusion a little more hope than the novel might have, viewers hoping for a blissful escape from the harshness of reality will most likely leave the theater disappointed.

Even Seyfried, whose wide-eyed innocence lends her character an unfailingly likeable quality, admitted that the film might be a little too sober for its February release.

“I’d make it happier,” she said, when asked how she would change the story if given the opportunity to direct it. “I was so depressed after I saw the first cut.”

As for real-life love letters, Seyfried still reads the one she received from an old boyfriend.

“It was the most romantic thing anyone’s ever written to me,” she said.
Although Tatum himself has never received a love letter, he had some solid advice for his fellow men:

“Guys, listen, if you haven’t written a love letter in a long time, you don’t have to sit and mail it. You don’t have to do anything, just write,” he said. “Wherever your loved one is, write her something.”

— Contact Franchesca Winters