The first ship to be torpedoed by an aircraft was an Ottoman steamer supplying troops during the Gallipoli Campaign. On 12 August 1915 a Short 184 seaplane flown by Flight Commander Charles Edmonds took off from the seaplane carrier HMS Ben-my-Chree in the Gulf of Xeros carrying a 14 inch torpedo.
He spotted a merchant ship and dropped his torpedo from an altitude of 15 feet and a range of 300 yards. It struck the ship abreast the mainmast, sending up a large amount of debris and water. Edmonds saw that the steamer was settling by the stern. It was subsequently discovered that the ship had been beach four days earlier after being torpedoed and shelled by the submarine HMS E14, captained by Lieutenant-Commander Edward Boyle VC.
Edmonds torpedoed another enemy ship 5 days later when he launched a torpedo from an altitude of 15-20 feet and a range of 800 yards that struck one of three Ottoman steamer bringing supplies and reinforcements to Gallipoli. The ship caught fire and had to be towed to Istanbul.
On the same day Flight Lieutenant G. B. Dacre was forced to land on the sea near an enemy hospital ship by engine trouble. He persuaded the ship that he was a friend with a wave. His engine was working well enough to taxi, so he headed off on the surface. He spotted and approached a large steam tug, fired his torpedo and scored a hit. He came under rifle fire, but was able to take off after a two mile run, returning to Ben-my-Chree. The tug sank.
During the Gallipoli Campaign, Royal Naval Air Service aircraft made 70 attacks on enemy ships with torpedoes and bombs. These helped the attempts by submarines to shut down Ottoman seaborne supplies to Gallipoli. The main problem was that the Short 184 seaplane could only take off with a torpedo if conditions were ideal: a calm sea with a slight breeze and an engine that was in perfect working order. Even then, they could carry enough fuel for only a 45 minute flight when armed with a torpedo. The performance figures quoted in the Wikipedia page linked in the first paragraph are for a later model with a 260 horse power engine. Ben-my-Chree carried the first Short 184s built.
R. D. Layman points out in his history of Naval Aviation in the First World War that it is impossible to indentify the Ottoman ships involved or to be sure of how badly damaged they were because no accurate list of all Ottoman merchant ships sunk during the war is available. It appears from the British reports, however, that all three ships were attacked and at least damaged.
HMS Ben-my-Chree belonged to the Isle of Man Steam Packet Company before the war: her name means Woman of My Heart in Manx. She was requisitioned by the Admiralty and converted to a seaplane carrier in 1915. She carried 4 seaplanes and was capable of 24.5 knots, making her the fastest of the merchantmen converted to seaplane carriers by the RN. She was sunk by Ottoman onshore artillery on 11 January 1917.
Edmonds served in the Royal Air Force after the war, rising to the rank of Air Vice Marshal during the Second World War. He had previously been awarded the Distinguished Service Order for his part in the Cuxhaven Raid on 25 December 1914.
 The above is based on W. A. Raleigh, H. A. Jones, The War in the Air: Being the Story of the Part Played in the Great War by the Royal Air Force, 7 vols. (Oxford: Clarendon Press, 1922). vol. ii, pp. 64-65.
 R. D. Layman, Naval Aviation in the First World War : Its Impact and Influence (London: Chatham, 1996), p. 149.
 Ibid., pp. 62-63.
 R. Gray, Conway’s All the World’s Fighting Ships, 1906-1921 (London: Conway Maritime Press, 1985), p. 68.