YF-110, YF-112, YF-113, YF-114, YF-116, and YF-118 - Captured/Obtained Soviet Aircraft flown by the US Air Force "Red Eagles"

Captured (or otherwise obtained) foreign aircraft used for evaluation and aggressor training were given designations in sequence using the pre-1962 "F-series." These aircraft were flown by the 4477th Test and Evaluation Squadron under the program "Constant Peg" from 1980-1988.

The aircraft were designated the following:

YF-110 - MiG-21 

YF-112 - Sukhoi Su-22

YF-113 - MiG-23

YF-114 - MiG-17

YF-116 (rumored) - MiG-25

YF-118 (rumored) - MiG-29

via Wikipedia, Area 51 - Black Jets (Google Books), and the 4477th Red Eagles Alumni Association.