The 12.8 cm FlaK 40, was a German World War II anti-aircraft gun. Although it was not produced in great numbers, it was one of the most effective heavy AA guns of its era. Development of the gun began in 1936, with the contract being awarded to Rheinmetall Borsig, the first prototype gun was delivered for testing in late 1937 and completed testing successfully. The gun weighed nearly 12 tonnes in its firing position, with the result that its barrel had to be removed for transport. Limited service testing showed this was impractical, so in 1938 other solutions were considered.