Also referred as a ballista, this crossbow would of been huge. Two men had to operate it to fullly draw it back. It had to be cocked back by a worm gear, which made it easier to draw it back. Then you would fire it by hitting a release catch with a hammer. This machine could of caused some real damage in a battle and even tipped the scales.
Leonardo also made his version of a helicopter. He drew it in 1493, also most 500 years before the actual helicopter was invented. The original design was made of reeds and had 2 meter blades. This idea would of been tremendous for war. supplies could be given by air, bombs could of been dropped by air, and many more ideas war-related.
Leonardo Da Vinci was the first to ever think of a tank. It had cannons all around its outer shell. The purpose of it was to be driven straight into battle and kill anything around it. Leonardo took inspiration from a turtle with his hard shell. Also its shape made it easier for objects to bounce off its "shell". The tank was operated by four men using hand cranks to turn the wheels. If this was invented during his time period it was of drastically changed future wars.