It’s been nearly 20 years since Daniel Murphy was told his son Michael, a Navy SEAL Lieutenant from Long Island, had been killed in action in Afghanistan — along with two team members and 16 other military personnel.

While the Medal of Honor recipient’s heroics were memorialized in the 2013 film “Lone Survivor,” his proud dad has spent almost every day sharing his legacy at the Lieutenant Michael P. Murphy Navy SEAL Museum in West Sayville since its opening two years ago.

“If Michael’s story brings the attention of the public to our fallen heroes, then he has accomplished something — even in death,” Murphy, now 77, told The Post. “It was our goal to tell people and show people what these incredible young men do.”

The semi-retired Murphy, who moved to Wading River to be near Michael’s grave at nearby Calverton National Cemetery, makes the 45-minute trip to the museum most days — not only to honor Michael’s legacy, but to discuss the sacrifices made by members of the armed services.

Along with giving visitors a profound sense of what life in the Navy SEALs and all military service is truly like, it’s a moment to reconnect with his late son.

“I tell him what’s going on, who is in the museum, who I met, what we’ve discussed, and things like that,” he said.

‘Lone Survivor’

On a typical day, Murphy speaks to visitors and vividly describes what he and his ex-wife, Michael’s mother, Maureen — who also visits the museum multiple times a week — have endured since their son’s death.

“We’ve had visitors from 47 states and 36 counties and just about all of them know Michael’s story coming in,” Murphy said.

The world knows of Murphy’s heroics from the blockbuster film in which Taylor Kitsch depicted the 29-year-old sacrificing himself as his four-man team was surrounded on three sides by dozens of Taliban militia on a 10,000-foot elevation — during a reconnaissance mission gone wrong in June 2005.

“Michael was a hero before he was a hero,” he said. “He had such a higher sense of purpose, there was this bright line between right and wrong. That is how he got the name ‘the Protector.'”

But Murphy’s father, an Army veteran who served in Vietnam, remembers plenty about his son that the public may not know.

“In eighth grade he got himself involved in an altercation with three bullies who tried to shove a special needs student into a gym locker. He knew it wasn’t right and he got involved,” Murphy said.

The Sayville museum — close to Murphy’s childhood home in Patchogue — focuses on the history of the elite Sear, Air, and Land fighting force since its World War II inception.

It spans to modern times, including an exhibit on the killing of Osama Bin Laden and the beyond-rigorous basic underwater demolition SEAL training (BUD/S) all recruits must pass — its brutality shown during the opening of “Lone Survivor.”

There’s a separate room dedicated to Murphy and his 18 comrades who also fell during the notorious Operation Red Wings near Asadabad.

Daniel and Maureen spend much of their time sharing heart-wrenching details of the several days they were waiting in limbo, with Navy SEALs living with them to get real-time updates on Michael’s fate.

Although the official word Murphy was killed in action came in the late hours of July 4, his father knew sooner.

“I remember [the SEAL] mentioning that an emergency beacon was going off with regard to one individual being alive,” he recalled.

“I remember turning to Maureen at that point and just saying, ‘You know, if there’s only one survivor, it’s not going to be Michael. It’s not his way for him to survive and lose all his men.'”

Continuing the mission

The creation of the museum helped Michael’s father see firsthand just how beloved his son was, especially when tradesmen across Long Island reached out in unison to volunteer their services toward its construction. “We basically built a $5 million museum for under $2 million,” Murphy, also a board member, revealed.

During construction seven years ago, the thought of giving back was strong in the mind of Chris Wyllie, a former SEAL and Special Warfare Combat Crewmen in the 1990s. Wyllie offered the pro bono help of an audio-visual company he opened after serving.

As he fostered a relationship with the Murphy family, learning more about Michael’s life story inspired Wyllie to become its executive director.

“It’s a different type of museum for how personal it is,” Wyllie, 51, told The Post, adding that Marcus Luttrell, the Navy SEAL lone survivor played by Mark Wahlberg, has attended some of their major events.

“I can speak about what everyone is experiencing at the museum. I think that brings it to an entirely new level,” he said.

About a year before 9/11, Wyllie had medically retired from the SEALs. Despite his best efforts, he could not rejoin any military branch as the war on terror began.

Although it took him a long time to come to terms with his situation, Wyllie has learned that he can provide a different kind of service in his current role — especially to visiting veterans showing signs of struggling.

“I make a personal effort to go over to them and say that I’m here, that they’re not alone in this, that I still experience stuff connected to PTSD,” he said.

“Nine times out of 10, I will give them my cellphone before they leave and say, ‘Listen, if you need anything, I don’t care if it’s 2 in the morning, you can call me’ because I’d rather have somebody wake me up that I could talk to and help.”

Just as the living continue to do good work in Michael’s name, Murphy is reminded at times that his son is there looking out, protecting — still.

In the late 2000s, a New Jersey friend of the family named a decommissioned Coast Guard boat he bought the Lieutenant Michael P. Murphy Medal of Honor.

“When the Miracle on the Hudson happened, it was the first boat that got to the plane,” Murphy said of the sensational 2009 incident that rocketed pilot Chesley “Sully” Sullenberger to stardom.

“On TV, someone said ‘It appears Lieutenant Michael Murphy is still on duty, saving lives.’ It just floored me.”