WASHINGTON — The Navy said Tuesday it is investigating about 30 senior sailors linked to alleged cheating on tests meant to qualify them to train others to operate naval nuclear power reactors. Representing roughly one-fifth of the reactor training contingent, sidelining 30 may put a pinch on the Navy’s training program, senior officials said.

It is the second exam-cheating scandal to hit the military this year, on top of a series of disclosures in recent months of ethical lapses at all ranks in the military.

Unlike an Air Force cheating probe that has implicated nearly 100 officers responsible for land-based nuclear missiles that stand ready for short-notice launch, those implicated in the Navy investigation have no responsibility for nuclear weapons. The Air Force probe is centered on Malmstrom Air Force Base, Mont., but could spread to its two other nuclear missile bases in North Dakota and Wyoming.

The Navy said the implicated sailors are accused of having cheated on written tests they must pass to be certified as instructors at a nuclear propulsion school at Charleston, S.C. The Navy uses two nuclear reactors there to train sailors for duty aboard any of dozens of submarines and aircraft carriers around the world whose on-board reactors provide propulsion. They are not part of any weapons systems.

The accused sailors previously had undergone reactor operations training at Charleston before deploying aboard a nuclear-power vessel. In the normal course of career moves, they returned to Charleston to serve as instructors, for which they must pass requalification exams.

Adm. John Richardson, director of the Navy’s nuclear propulsion program, said an undisclosed number of senior sailors are alleged to have provided test information to their peers. He was not more specific, but one official said the information was shared from the sailors’ home computers, which could be a violation of security rules because information about nuclear reactors operations is classified.

“That’ll be an active part of the investigation to fully understand” the extent of any security rule violations, Richardson said.

Richardson said the alleged cheating came to light Monday when a senior enlisted sailor at the Charleston training site reported the cheating to higher authorities. Richardson said the unidentified sailor “recognized that this was wrong” and chose to report it.

The matter was still under investigation by the Naval Criminal Investigative Service.

Adm. Jonathan Greenert, the chief of naval operations, told reporters at a Pentagon news briefing, where he was accompanied by Richardson, that he was upset to learn of the breakdown in discipline.

“To say I am disappointed would be an understatement,” Greenert said. “We expect more from our sailors — especially our senior sailors.”

Neither Greenert nor Richardson identified the rank of the alleged cheaters but described them as senior enlisted members. There are about 150 nuclear power reactor instructors at the Charleston site. With about 30 of them banned, at least temporarily, from performing their duties, the training program might suffer.

“I could possibly foresee an impact in Charleston,” Richardson said. “We’ll see if that is broader.”

Pressed to say how many sailors were implicated in the investigation, Richardson said a “ballpark figure” was something like 12 to 20. But a short time later another Navy official said the number was approximately 30 but could change as the investigation unfolds. The official spoke on condition of anonymity because the official was not authorized to discuss publicly any details beyond what Richardson and Greenert disclosed at their news conference.

Richardson said he could not discuss possible disciplinary action against those involved because the probe was ongoing. However, he said that anyone in the naval nuclear power program — either in a training setting or aboard a ship at sea — who is caught cheating would usually be removed from the program and “generally” would be kicked out of the Navy.

The decision to have Greenert and Richardson announce the cheating investigation publicly was a sign of how seriously the Navy takes the matter.

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Associated Press writer Lolita C. Baldor contributed to this report.