The first tanks, beginning with the British Mark I launched against the German trenches in World War I, were nearly impregnable to ordinary rifle fire. Most armoured cars were similarly protected, but troops rarely faced armoured cars, as they could not navigate the landscape of trench warfare very well. Though tanks and armoured cars were vulnerable to artillery, mortars, and grenades, infantry was at a significant disadvantage when facing armoured fighting vehicles since they had no effective direct fire weapon, with the exception of the ubiquitous trench mortar, improvised on the spot. In the direct fire mode, this weapon was manhandled by German infantry over the front of a trench wall and fired at low angles by eye at approaching enemy vehicles. Though somewhat effective, these actions were obviously very hazardous to any desperate mortar crew as their exposure could attract enemy fire.