Machine Gun Machine guns of all armies were largely of the heavy variety and decidedly ill-suited to portability for use by rapidly advancing infantry troops. The 1914 machine gun, usually positioned on a flat tripod, would require a gun crew of four to six operators. Could fire 400-600 small- calibre rounds per minute a figure that was to more than double by the war's end, with rounds fed via a fabric belt or a metal strip. http://www.firstworldwar.com/weaponry/machineguns.htm
Ross Rifle The Ross had many faults in trench warfare, and after numerous complaints the replacement of all Ross rifles in the three Canadian Divisions by the Lee Enfield was ordered. With its ten-cartridge magazine, the Lee Enfield was well suited to rapid fire; a suitably trained soldier could expect to fire twelve well-aimed shots a minute. The Lee-Enfield proved so sturdy and reliable that its use continued into World War Two.
Chlorine Gas The debut of the first poison gas came on 22 April 1915, at the start of the Second Battle of Ypres. The types of protection initially handed out to the troops around Ypres following the first use of chlorine in April 1915 were primitive in the extreme. 100,000 wads of cotton pads were quickly manufactured and made available. These were dipped in a solution of bicarbonate of soda and held over the face. Soldiers were also advised that holding a urine drenched cloth over their face would serve in an emergency to protect against the effects of chlorine.
Tanks Tightly fitting 3 men inside, conditions for the tank crews were also far from ideal. The heat generated inside the tank was tremendous and fumes often nearly choked the men inside. This first tank was given the nickname 'Little Willie' (soon followed by 'Big Willie') and, as with its predecessors, possessed a Daimler engine. Weighing some 14 tons and bearing 12 feet long track frames. Top speed was three miles per hour on level ground, two miles per hour on rough terrain They often broke down and became ditched - i.e. stuck in a muddy trench - more often than anticipated (ex. Passchendaele Battle)
Flamethrowers The basic idea of a flamethrower is to spread fire by launching burning fuel (such as coal or sulphur).
Artillery (large calibre guns) There were many different kinds of artillery (11) in WWI. For example, the German howitzer Big Bertha could shoot 2,200lbs shells over 9 miles! She took a crew of 200 men over 6 hours to assemble and disassemble her.
Trench Mortar A mortar is essentially a short, stumpy tube designed to fire a projectile at a steep angle (by definition higher than 45 degrees) so that it falls straight down on the enemy. Lighter more mobile than large artillery. The Stokes mortar could fire as many as 22 bombs per minute and had a maximum range of 1,200 yards.