Place 10 Martian Walkers in a random area. Walkers are amphibious, moving 2. In combat they can fight 2 different ways, either hitting like an AA Gun (but against every unit), or launching a normal strength 6 attack. Martians never capture Factories and AA guns, they are simply considered normal units that can be hit. Martians are not destroyed if hit, they simply retreat. They can only be destroyed if hit and they have nowhere to retreat.
Martians do not build new units or collect income.