 They were slow (men could run, and frequently walk, faster); vulnerable (to artillery) due to their size, clumsiness and inability to carry armour against anything but rifle and machine gun ammunition; extremely uncomfortable (conditions inside them often incapacitating crews with engine fumes and heat, and driving some mad with noise); and often despicably unreliable (frequently failing to make it to their targets due to engine or track failures).This was the factor behind the seemingly mindless retention of large bodies of cavalry, which even in 1918, with armies incompletely mechanised, were still the only armed force capable of moving significantly faster than an infantryman on foot.It was not until the relevant technology (in engineering and communications) matured between the wars that the tank and the airplane could be forged into the co-ordinated force needed to truly restore manoeuvre to warfare.