No, armoured tanks were not invulnerable to machine guns. Early tanks, such as the British Mark I, were susceptible to heavy machine gun fire. Their armour was often too thin to stop bullets from large calibre machine guns, such as the German MG08. As tanks developed, their armour became thicker, making them more resistant to machine gun fire. However, even modern tanks can be vulnerable to armour piercing rounds from large calibre machine guns.