Sherry Sullivan can remember childhood vacations in Allagash when her dad would fly his plane under the St. John River Bridge.

Daredevil aerobatics aside, Geoffrey Sullivan was also an ardent cold warrior who disappeared without a trace 40 years ago – allegedly while flying on a covert mission to Cuba.

The official story is that Sullivan’s plane dropped off the radar screen somewhere over Central America, but his daughter is convinced he ended up in a Cuban jail and was killed as a spy.

“I believe that my father was executed,” Sullivan, 48, said Thursday from her home in Stockton Springs. “It would be very selfish to say I wished my father was alive and had been in a Cuban prison for 40 years. I’ve met men who have been in prison in Cuba. They’re free, but they’re not all there. It was probably better that my dad was executed. He probably stood tall and proud. He was very patriotic.”

On Sunday, Sullivan will mark the 40th anniversary of her father’s death at the Veterans Memorial Cemetery in Augusta. The 2:30 p.m. ceremony will take place in the Garden of Remembrance, which is dedicated to veterans missing in action. Representatives of Sen. Susan Collins and Gov. John Baldacci will attend the gathering along with a number of armed forces veterans. A group of drummers from the Penobscot Nation will perform at the ceremony.

Not knowing the fate of her father – for certain – has haunted Sullivan for more than two decades. She has thousands of pages of documents obtained from the U.S. government in an attempt to track his life.

But the world of covert operations is a shadowy one, and prying information from secret agencies is difficult.

Sullivan fought her battles all the way to federal court in Boston, but was stymied in the end by a government opposed to opening up some files to prying eyes.

“They said it was a matter of national security,” Sullivan said. “The government never came to admit that my father had worked for any government agency.”

Sullivan’s search for information did yield something solid: She isn’t alone.

She established an organization, Forgotten Families of the Cold War, that is dedicated to the surviving families of people missing in action or believed held prisoner during the Cold War era.

That era, from the end of World War II in 1945 through the collapse of the Soviet Union in 1991, contains numerous mysteries about individuals and groups, legal and illegal, whose activities are only gradually being explained as archives and documents are declassified or studied in the United States and elsewhere.

On Monday and Tuesday, Forgotten Families will hold its first conference at the Penobscot Bay Gallery in Stockton Springs. The two-day gathering will feature talks and remembrances by those whose fathers disappeared during operations in and over Cuba.

“It’s been a long time trying to get these families together,” Sullivan said.

In some respects, the Cold War between the United States and Cuba is still under way.

Most of the members of Sullivan’s group are linked through some sort of alleged covert operations in or around Cuba and Latin America in the late 1950s and early 1960s. Communist leader Fidel Castro took power in Cuba in 1959 and is the country’s president today.

The last known sighting of Geoffrey Sullivan was in 1963 when he took off in a twin-engine Beechcraft with New York newspaperman Alex Rorke Jr., who was believed to be an operative of the Central Intelligence Agency who ran guns to Cuba.

A month earlier, Sullivan and Rorke had allegedly taken part in a bombing run over Cuba in a refurbished B-125 bomber. That daring act received widespread newspaper coverage and both men were identified as being involved.

Sullivan has attempted for years to obtain information from the Rorke family, but his survivors have been reluctant to get involved.

There is an old saying about the world of espionage that those who know don’t say and those who say don’t know. Sullivan said she has found it difficult to find solid information under such murky circumstances.

She said her father and the others were wrapped up with shady characters and groups.

South Florida in the early 1960s was a hotbed of training camps for paramilitary groups aimed at removing Castro. Though some apparently were sanctioned by the U.S. government, many of their actions were illegal and the official stance was to deny everything.

Some of the people Geoffrey Sullivan encountered would later turn up during the investigations of the assassination of John F. Kennedy and the Watergate burglary, Sullivan said. She has shelves of books in which her father and Rorke are mentioned in connection with the investigations.

“It was a dangerous time. Covert operators were all over the place and the funding was coming from all directions. You had money coming from the government, the Mafia and Cuban exiles,” she said. “There were a lot of flights over Cuba: bombings, arms drops, leaflets.

“I firmly believe the government knew my father was in a Cuban prison and not only did they do nothing about it, they covered it up.”

Geoffrey Sullivan was not from Maine, but had family in the state. He had served in the Air Force during the Korean War and was a member of the Army Reserves when he and Rorke left on a flight on Sept. 23, 1963.

Although the government has never confirmed he was in the Army at the time of his disappearance, Sullivan has her father’s honorable discharge, which was issued six months after he went missing.

Sullivan said it wasn’t until last fall that the Department of Veterans Affairs listed her father as “missing in action.” She said the VA provided her with the marker that will be placed in the Augusta cemetery.

“I feel my father has finally been recognized by some government agency, and to me that’s a big deal,” she said. “In some ways my father wasn’t real to me because he was so dramatic and daring. He was like a movie star in my mind, and then it was like he was dropped into a void.

“I’m writing a book about my experiences and I’m going to call it ‘Chasing Dad’s Shadow.’ Ever since I was a kid I felt he was that close, but really it’s like a shadow. It’s all so unreal.”

Forgotten Families of the Cold War may be reached at www.forgottenfamilies.com.