61-2667 was upgraded to a WC-135W, given the project name Constant Phoenix, and remains in service with the 45th Reconnaissance Squadron at Offutt Air Force Base, Nebraska.

[10] In June 2022, the first of three planned WC-135R aircraft (serial number 64-14836) completed its maiden test flight, and was delivered to the 55th Wing on 11 July 2022.

[11][12] The other two were delivered in May 2023 (tail number 64-14831)[13] and December 2023 (tail number 64-14829)[1] The WC-135B, WC-135W, and WC-135R Constant Phoenix atmospheric-collection aircraft support national-level intelligence consumers by collecting particulate debris and gaseous effluents from accessible regions of the atmosphere in support of the Limited Nuclear Test Ban Treaty of 1963.

The information collected by the aircraft is utilized by Detachment 1 of the Air Force Technical Applications Center's 21st Surveillance Squadron.

[1] The Constant Phoenix's modifications are primarily related to the aircraft's on-board atmospheric collection suite, which allows the mission crew to detect radioactive debris "clouds" in real time.

The interior seats 33 people, including the cockpit crew, maintenance personnel, and special equipment operators from the Air Force Technical Applications Center.

General characteristics Performance WC-135B aircraft flew 25 sorties in 1979 to try to ascertain whether a double flash in the South Atlantic that was detected by a Vela satellite was a nuclear weapons test;[19] however, the result was inconclusive.

On October 9, 2006, North Korea's official Korean Central News Agency (KCNA) reported that the country had performed a successful underground nuclear test.

The national intelligence office statement said the air samples were collected Wednesday, and analysis found debris that would be consistent with a nuclear test 'in the vicinity of Punggye' on Monday.

"[21] On November 23, 2010, Sankei Shimbun reported that a WC-135 had been moved to Kadena Air Base in September 2010, in anticipation of a North Korean nuclear test.

[22] On January 31, 2013, the WC-135W was reported to be conducting surveillance flights out of Kadena Air Base in anticipation of another North Korean nuclear test.

It was conjectured that this came in response to several reports of anomalous levels of iodine-131 coming from the Norwegian-Russian Border, but as of April 10, 2017, there was no official cause of the iodine-131 release.