For the allies it was becoming clear that the recent blockades had been a complete failure and that an attack by land would be impossible. Ideas were put forward to break the siege once and for all. The plan was proposed that a squadron of battery ships should take on the British land-based batteries and pound them into submission by numbers and weight of shots fired, before a storming party attacked from the siege works on the Isthmus and further troops were put ashore from the waiting Spanish fleet. The French engineer Jean Le Michaud d'Arçon invented and designed the floating batteries—'unsinkable' and 'unburnable'—intended to attack from the sea in tandem with other batteries bombarding the British from land.