The First Army was a formation of the British Army that existed during the First and Second World Wars. The First Army included Indian and Portuguese forces during the First World War and American and French units during the Second World War.

The Portuguese Expeditionary Corps was the main military force from Portugal that fought in the Western Front, during World War I. Portuguese neutrality ended in 1916 after the Portuguese seizure of German merchant ships resulted in the German Empire declaring war on Portugal. The expeditionary force was raised soon after and included around 55,000 soldiers.