23 March 1940 commissioned Second Lieutenant, Grenadier Guards, later that year joined No.8 Commando. Embarked for the Middle East.  Later joined the SBS.

"In support of a vital convoy due at Malta from Gibraltar in mid August 1942, a commando raid was planned to destroy Junkers 88 bombers on Catania Aerodrome, Sicily. Three officers and three other ranks landed on the night of August 11th-12th 1942 in poor weather conditions on a defended beach. The party penetrated to the airfield to find armed sentries on every aircraft. After reconnoitering for four hours they were detected but whilst retiring used their explosive to destroy some electric power pylons.

During the withdrawal to the beach Sergeant Dunbar was wounded and taken prisoner. The remaining five were unable to find HMS UNA at the rendezvous and one canoe capsized; they were taken prisoner after daylight some five miles out to sea.

Buchanan showed courage and resource of a very high order. The raid was carried out with great determination and although the objective was not achieved due to the enemy's exceptional precautions the boldness and initiative shown deare considered most deserving of recognition. When one canoe capsized after searching for UNA after withdrawal Buchanan endeavoured to swim 5 miles to shore to obtain aid for the remaining 4 persons. He was taken prisoner near the shore by a fishing vessel. Buchanan escaped from prison in Italy and crossed the British lines after 8 months in hiding."