The STG-44 from WWII, It was also the first automaitc rifle and then later they made the automat kalashnikov which looks similar to the STG-44. I think the Germans made all of the best weaponry like the world's first jet powered aricraft(Me 262); Sadly they started using the STG-44 later in the war then at the begining. They had also invented a saucer type of aircraft toward the very ending of the war after the jet. Just image if the war had lasted a little more long, they might have improved everything and mass produced them or maybe even thing of new inventions.
Me 262 -
STG44 -