Was Winston Churchill prime minister in World War 1?

Yes. Churchill was the First Lord of the Admiralty, the civilian head of the Royal Navy. As such he championed the Gallipoli campaign in Turkey, which ended in disaster. As a result he had to resign from the Admiralty. Churchill had been educated at Sandhurst, the British equivalent of West Point. He obtained a commission as a battalion commander and went to France and served in the trenches for about a year. Then he became Minister of Munitions, a different cabinet position, overseeing production of the vast amounts of war materials and equipment necessary. Few men contributed more to the war effort than Churchill.