They beat Plows into Swords--Male and Female They Created Them

By 1915 the ground war on the Western Front was so entrenched that the British Admiralty, seeking to break the stalemate, developed what were first known as "landships" but which later came to be known by their covert name--tanks. The idea was to develop a machine that could traverse craters, barbed wire, trenches, and bring firepower directly behind enemy lines.

The first landships used a British superstructure atop an American track and chassis built by a Chicago company and originally designed for plowing fields. Early testing and improvements quickly led to a more advanced prototype named "Mother." Her parallelogram-shaped tracks maximized trench crossing and her gun-bearing sponsons, a design borrowed directly from warships, added to her chimerical appearance. The hermaphrodite Mother gave birth to "male" and "female" varieties which were first battle-tested at the Battle of the Somme in 1916.

Male and female variety tanks differed depending on what protruded from the sponsons. Males had the big guns--naval 6 pounders, while females had water-cooled Vickers or Maxim machine guns (two on each side, four total). The reason for the females was an acute shortage of bigger guns. The differences are apparent in this graphic:

Female (top) and male (bottom) Mark I
 Tanks