It's P-47: The Freedom Fighter, the PCE home version of the arcade's P-47 Thunderbolt: The Freedom Fighter. Honestly, given with how cheerfully peppy the music is the name change makes sense. Blue skies, lovely sunsets, scenic mountains... it's supposed to be based around France during the Second World War but it seems so damned happy. Bizarre. Also, the title screen is a cute little airshow of most of the planes and other aeronautical craft featured in-game.