In this file photo, the WC-135W Constant Phoenix aircraft performs touch ‘n go landing exercises at Offutt Air Force Base, Neb. (U.S. Air Force photo/Josh Plueger)

The U.S. Air Force will soon deploy a WC-135 Constant Phoenix aircraft to test for radiation near North Korea, part of the U.S. military’s ongoing effort to determine what the country’s provocative nuclear bomb test entailed.

The use of the so-called nuclear “sniffer plane” was confirmed on Tuesday by an official at the Pentagon, speaking on condition of anonymity due to the sensitivity of the operation. The aircraft collects air samples and debris, and is a modified version of a C-135B or EC-135C Boeing airplane. It will determine whether the explosion was actually a hydrogen blast, as North Korea has claimed. That assertion has been viewed with widespread skepticism by nuclear weapons experts.

“We’ll know for sure once the WC-135 gets air samples,” the defense official said.

The Constant Phoenix was commissioned by Army Gen. Dwight D. Eisenhower in September 1947, as he gave the Army Air Forces — a precursor of the Air Force — responsibility for detecting atomic explosions worldwide, Air Force officials said. The mission was initially assigned to the WB-29 aircraft, but was swapped over to WB-50 and eventually the WC-135 by 1965.

Air sample missions have been carried out routinely since, with the WC-135 playing a key role in tracking radioactive debris after the disaster at the Chernobyl nuclear plant in the Soviet Union in 1986, according to an Air Force fact sheet. The WC-135 is currently the only aircraft in the service carrying out air-sampling missions, with crews from the 45th Reconnaissance Squadron at Offutt Air Force Base in Nebraska typically manning them. Equipment on board is operated by members of the Air Force Technical Applications Center.

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The WC-135 typically flies directly through a potential radioactive plume, with protection from radioactivity incorporated into the plane so that airmen on board do not need to wear hazardous materials suits, said Susan Romano, a spokeswoman at Offutt Air Force Base for the testing center. She would not confirm the deployment of the WC-135, citing Air Force policy, but said that the testing center has recorded underground seismic activity in the area of where North Korea claimed the explosion occurred.

North Korea said it had successfully conducted a test of a miniaturized hydrogen nuclear device on the morning of Jan. 6, in an announcement broadcast on state-run television. (Reuters)

“At this point, we are unable to confirm North Korea’s claim of what the explosion was,” Romano said.

In another recent example of the plane’s use, the WC-135 was part of military operations over Japan in 2011 after the meltdown of nuclear reactors at the Fukushima power plant following an earthquake and tsunami.

Defense Secretary Ashton B. Carter spoke on Tuesday with Han Min-koo, South Korea’s minister of defense, following the report of the new test, said Pentagon press secretary Peter Cook.

“Secretary Carter reaffirmed the ironclad commitment of the United States to the defense of [South Korea], and that this commitment includes all aspects of the United States’ extended deterrence,” Cook said in a statement. “Minister Han emphasized the strength of the U.S.-ROK alliance and its vital role in assuring peace and stability on the Korean Peninsula and across the Asia-Pacific. Carter and Han agreed that North Korea’s provocations should have consequences.”

Thomas Gibbons-Neff contributed to this report.