The Navy disclosed Tuesday that it is investigating about 30 people on suspicion of cheating on exams to operate nuclear reactors, adding to a list of recent embarrassments that have tarnished the U.S. military’s nuclear forces.

Navy officials said they were tipped off the day before to the alleged ring of cheaters by a sailor at a nuclear-training program in Charleston, S.C. The program certifies operators of nuclear reactors that propel ships and submarines, a core job in the Navy for more than a half century.

Although the investigation does not involve nuclear weapons, the Navy probe echoes a similar, still-unfolding scandal inside the Air Force. Nearly 100 Air Force officers responsible for nuclear-armed missiles are likewise under scrutiny for allegedly cheating on qualification exams.

“To say that I’m disappointed would be an understatement,” Adm. Jonathan W. Greenert, the chief of naval operations, told reporters at the Pentagon. “The foundation of our conduct throughout the Navy is integrity. We expect more from our sailors, especially our senior sailors, and we demand it in our training and in our operations.”

The cheating revelations come as the Navy is still grappling with a separate scandal involving senior commanders accused of giving sensitive information to a foreign contractor in exchange for sex, money and other favors.

At Charleston, the allegations concern senior enlisted sailors who serve as instructors at a nuclear-power school. The instructors, who must periodically requalify as reactor operators and trainers, are suspected of sharing answers on an exam, said Adm. John M. Richardson, director of the Navy’s nuclear-propulsion program.

Richardson said the exams involve classified information and that the personnel suspected of cheating have had their access revoked to two nuclear reactors that are used for training at Charleston.

He declined repeatedly to say how many sailors are under scrutiny, saying that the investigation was in an early stage. Another Navy official, speaking on condition of anonymity because details of the probe remain confidential, said about 30 senior enlisted sailors have been implicated.

Richardson said the last comparable cheating incident involving the Navy’s nuclear forces occurred in 2010.

In that incident, officials discovered that sailors aboard the USS Memphis, a submarine, had circulated the answer key to a nuclear-proficiency test. Thirteen crew members were disciplined and the submarine’s commanding officer was fired.

Last month, Defense Secretary Chuck Hagel ordered two broad reviews of the military’s nuclear forces after a string of incidents involving Air Force officers and units.

Hagel also convened a special meeting of nuclear commanders — including Navy officials — at the Pentagon to examine “the health of the culture” of the nuclear force and come up with “an action plan” within 60 days.

Greenert, the Navy’s top admiral, said the service is still conducting its reviews in response to Hagel’s order. He did not indicate if any concerns other than the troubles in Charleston have surfaced so far.

In addition to nuclear reactors that power many of its vessels, the Navy is responsible for nuclear-armed missiles aboard some of its submarines.