Fifty years ago in 1969, on the 57th birthday of North Korean leader Kim Il Sung, a MiG 21 fighter jet vectored in on a U.S. EC-121 reconnaissance aircraft operating far outside the North’s territorial limits, firing two missiles that killed all 30 sailors and a Marine aboard the Navy plane.

It was 15 months after North Korea seized the USS Pueblo and 83 crew.

Newly elected President Richard Nixon had vowed there would be no “Pueblo” on his watch, and no incident in which a “fourth-rate” power would show such disrespect for the United States, according to the National Security Agency.

Nixon’s advisers contemplated retaliation against North Korea ranging from airfield bombings to all-out nuclear strike — and then did nothing.

It was an example of the vexing nature of North Korea then and now; U.S. military planners fretted that an attack on the North would unleash destruction on the South.

Fifty years later, the Navy on Monday remembered the human toll of the tragic mission, dubbed Deep Sea 129.

Twenty-one relatives of three fallen crew members traveled to Oahu and Ford Island for a memorial ceremony organized by Navy Information Operations Command Hawaii.

“Today is a solemn day as we gather to recognize and remember the 50th anniversary of the ultimate sacrifice our shipmates made in the line of duty,” said Capt. Madelene Means, head of NIOC Hawaii. “This happened over a year after the capture of the USS Pueblo and just months after the return of that crew to the United States.”

Means, who oversees cryptologic personnel who deploy on airborne reconnaissance missions around the Pacific, added that the shoot-down was “brutal and planned. There was never an apology. But we will honor the sacrifice. We will remember.”

Aside from the deliberations about what should be done following the downing of Deep Sea 129 was the shock and uncertainty experienced by the families of the missing.

Eileen Taylor, the wife of crew member Lt. Robert Taylor, who was living in Japan where the EC-121 was operating from, was pregnant and had boys 1 and 3.

“It was tough. I can’t imagine going through that,” said the oldest son, Michael, now 52.

Only two bodies were found.

“You had Russian ships there immediately, so (we) really didn’t know if they were alive or dead,” said the Chicago resident, who came with 11 family members. “A lot of going back and forth — were they taken prisoner? Are they somewhere?”

His father was a linguist who spoke Russian.

Retired Cmdr. Joe Overstreet, who followed his father, Lt. Cmdr. James Overstreet, into the Navy, said he was 6 years old when his mother told him and his brothers they would never again see their father, the mission’s commander.

“Shock and anger followed by deep, lonely grief, depression and survivor’s guilt were common effects that lasted decades for many surviving family members and close friends of the crew,” he told those present in his remarks as guest speaker.

About 150 sailors stood at attention during the ceremony in NIOC Hawaii’s building on Ford Island.

The Lockheed EC-121 Warning Star, with long-range radars above and below the fuselage, was a military surveillance version of the four-propeller Super Constellation, a graceful aircraft that sported triple tail fins.

By about 1960 there were some three dozen of the Constellation variants at Naval Air Station Barbers Point.

Deep Sea 129, with Fleet Air Reconnaissance Squadron 1 based in Japan, departed Naval Air Facility Atsugi on April 15, 1969. The shoot-down occurred at just over 100 miles from the coast of North Korea in the Sea of Japan.

The squadron had flown the mission — unescorted by fighters — for two years and was rated “minimal risk,” the Navy said. But there were warning signs, Overstreet said Monday.

The head of U.S. Forces Korea had sent a message to U.S. Pacific Fleet saying that in meetings the North had been “particularly heated and vicious” in warning United Nations forces about “provocative actions,” he said.

As the United States increasingly committed military forces to the Vietnam War in the mid- to late 1960s, the communist regime in North Korea exhibited growing hostility, according to the NSA.

After the downing, Nixon ordered an aircraft carrier task force south of the Sea of Japan. Documents declassified in 2010 showed that the administration developed more than two dozen plans for retaliation against the North, including using atomic weapons of 0.2 to 10 kilotons, the National Security Archive at George Washington University reported.

“Yet, in another pattern that would be repeated in the years since then, Nixon and his advisers were forced to heed the Pentagon’s warnings that anything short of massive attacks on North Korea’s military power would risk igniting a wider conflagration on the peninsula, leaving diplomacy, with all its frustrations, as the remaining option,” the archive noted.

Monday’s ceremony ended with a trek to Ford Island’s old seaplane ramps for taps, a gun salute and placement of a memorial wreath in Pearl Harbor.