The Messerschmitt Bf-109 was designed before WW2, and the earliest versions saw combat in the Spanish Civil War. It became the most widely used fighter in the Luftwaffe with 30,000 being produced in many variants and sub-variants.
The 109 was also used by at least ten other countries, but was out-classed by the end of the war, and only lived on as the Avia S-199 and Hispano HA1.112.
The 109 E-4 was armed with 2 x 13mm machine guns and 3 x 20mm cannon. Bombs, cameras and fuel tanks could be fitted to later versions and some guns would be removed in some cases.
This example is a Bf-109 E4 from 3/NJG1, circa 1941.