Tommy Atkins
Tommy Atkins (often just Tommy) is a term for a common soldier in the British Army.  The term was used in the 19th century, but it is particularly associated with World War I.  It can be used when talking about the soldiers, or when speaking to them. German soldiers would call out to "Tommy" across no man's land if they wanted to speak to a British soldier. French and Commonwealth troops would also call British soldiers "Tommies".