Two of the "Test Series" games released by Poultron Press, the forerunner of SPI. Flying Fortress was Test Series Game 2 and Flying Fortress II was Test Series Game 10. The games covered the Allied strategic bombing in Europe during World War II.
The games covered both US and British bombing efforts. Planes include B-17s, B-24s, Lancasters, and Halifaxes. (B-29s are in the optional rules.)
The games were reportedly the first to use hidden victory conditions (the "nidden victory points" mechanism is the closest available equivalent). Flying Fortress II may have been the first game with double-sided counters (the back used for step reduction).
Each turn in the game was a separate "tactical mission" game representing a month of real time. These turns were linked together to make a campaign. The mission game rules were divided into basic, standard, and advanced levels.