The military tank was first developed by:

The foundational concept here is the history of military technology and the origins of the tank.

• Britain is the correct answer. The first operational military tanks were developed by Britain during World War I. The prototype, known as 'Little Willie,' was built in 1915, and the Mark I tank saw its first combat action in September 1916 at the Battle of the Somme.
• Germany developed tanks later in the war, but they were not the first to do so.
• The US and Russia also developed their own tank designs, but their initial efforts and deployments came after Britain's pioneering work in this field.

Therefore, Britain holds the distinction of being the first country to develop and deploy the military tank.