Hagel placed the calls from aboard the military command aircraft that carried him home yesterday from an international security conference in Germany.
The Pentagon chief spoke to six Minuteman 3 missile launch control officers at centers operated by the 341st Missile Wing at Malmstrom Air Force Base in Montana.
Malmstrom is the focus of a widening investigation into alleged cheating by launch officers on proficiency tests.
About half of the entire cadre of missile launch officers at Malmstrom have been removed from duty because of the accusations, and the probe is continuing.
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A defence official who briefed reporters on Hagel's phone calls said the six officers to whom he spoke were generally positive in their outlook but also cited strains and stresses.
The official was not authorised to discuss the private conversations by name and spoke on condition of anonymity.
Hagel told the officers about a meeting he conducted Wednesday at the Pentagon with top Air Force and Navy officials to discuss problems within the Air Force nuclear missile force.
Hagel also thanked the officers for taking on the extra shifts required while more than 90 of their colleagues are suspended in the cheating probe. Hagel expressed confidence in their ability to execute the mission, the defence official said.