the same space as the engine. The environment inside was extremely unpleasant; since ventilation was inadequate, the atmosphere was contaminated with poisonous carbon monoxide, fuel and oil vapours from the engine, and cordite fumes from the weapons. Temperatures inside could reach 50 °C (122 °F). Men sometimes lost consciousness inside the tank but more often collapsed when getting out into fresh air. The symptoms were suggestive of carbon monoxide poisoning but the high temperatures inside together with humidity were also identified as a possible cause To counter the danger of bullet splash or fragments knocked off the inside of the hull, crews were issued with leather-and-chainmail masks. A leather helmet was also issued, to protect the head against projections inside the tank. Gas masks were standard issue as well, as they were to all soldiers at this point in the war due to use of chemical weapons by both sides. The side armour of 8 mm initially made them largely immune to small arms fire, but could be penetrated by the recently developed armour-piercing K bullets (introduced mid-1917). There was also the danger of being overrun by infantry and attacked with grenades. The next generation had thicker armour, making them nearly immune to the K bullets. In response, the Germans developed the 13.2 mm Mauser 1918 T-Gewehr anti-tank rifle (introduced in mid-1918), and also a Geballte Ladung ("bunched charge") – several Stielhandgranate stick grenades bundled together for a much bigger explosion. A near hit by an artillery or mortar shell could cause the fuel tanks (which were placed high in the front horns of the track frames either side of the drivers' area, to allow gravity feed) to burst open; a direct hit by any sort of artillery shell was more than enough to penetrate the armor and destroy the vehicle. Incinerated crews were removed by special Salvage Companies, who also salvaged damaged tanks. Steering was difficult, controlled by varying the speed of the two tracks. Four of the crew, two drivers (one of whom also acted as commander; he operated the brakes, the other the primary gearbox) and two "gearsmen" (one for the secondary gears of each track) were needed to control direction and speed, the latter never more than a walking pace. As the noise inside was deafening, the driver, after setting the primary gear box, communicated with the gearsmen with hand signals, first getting their attention by