Complex sentence: They were first deployed in 1916 at the Battle of the Somme in limited numbers, proving unreliable and ineffective at first, as mechanical and logistical issues overshadowed implementing a coherent tank doctrine.
Split into simpler sentences: They were first deployed in 1916 at the Battle of the Somme in limited numbers. Tanks proved unreliable and ineffective at first, as mechanical and logistical issues overshadowed implementing a coherent tank doctrine.