The Mark I was a rhomboid vehicle with a low centre of gravity and long track length, able to negotiate broken ground and cross trenches. Main armament was carried in sponsons on the hull sides.
The hull was undivided internally; the crew shared 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). Entire crews lost consciousness inside the tank or, sometimes, collapsed when again exposed to fresh air.
To counter the danger of bullet splash or fragments knocked off the inside of the hull, crews were issued with leather-and-chainmail masksand a leather helmetwas 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 (see Chemical warfare)
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 hitting the engine block with a heavy spanner. For slight turns, the driver could use the steering tail: an enormous contraption dragged behind the tank consisting of two large wheels, each of which could be blocked by pulling a steel cable causing the whole vehicle to slide in the same direction. If the engine stalled, the gearsmen would use the starting handle – a large crank between the engine and the gearbox. Many of these vehicles broke down in the heat of battle making them an easy target for German gunners. There was no wireless( radio); communication with command posts was by means of two pigeons, which had their own small exit hatch in the sponsons, or by runners. Because of the noise and vibration, early experiments had shown that radios were impractical, therefore lamps, flags, semaphore, coloured discs, and the carrier pigeons were part of the standard equipment of the various marks.