The 'female' version of the MkI tank was produced in larger numbers than it's 'male' partner due to the fact that the four Vickers machine guns mounted on the sides were found to be more effective in combat than the heavier guns carried by the 'male' in the trecherous conditions on the Western Front. The British Army soon learnt how effective these new weapons could be in both attack and in protecting advancing troops using the tank as a shield.