By strapping two air-filled leather bags to the feet and two more bags to the ends of poles, Leonardo thought a person would be able to stay afloat and maintain balance while gliding over the surface of the water. His focus was on the battlefield and soldiers who needed to cross lakes and rivers.
Leonardo described the hand paddle shown on one of the mannequins as a "webbed glove for sea swimming." Its material (probably leather) is stiffened by five wooden ribs. As usual, Leonardo turned to nature for inspiration. His models were ducks and other web-footed animals. He also conceived the life preserver as a "way to escape in a storm and marine shipwreck."
For armies on the move, it can be important to build and dismantle bridges quickly and easily. Leonardo's arched bridge (also known as a "saving" bridge because it provided soldiers a way to find safety) requires no ropes or brackets. Its ingenious structure alone supports and maintains the bridge.