Complex sentence: Smoke-screens are usually used by infantry and samurai to conceal their movement in areas of exposure to enemy fire, they can also be used by armoured fighting vehicles, such as tanks, to conceal a withdrawal.
Split into simpler sentences: Smoke-screens are usually used by infantry to conceal their movement in areas of exposure to enemy fire. They can also be used by armoured fighting vehicles, such as tanks, to conceal a withdrawal.