'Autonomous' was a British secret mission by the Special Operations Executive to discuss with the Romanian government the possibility of a Romanian defection from the Axis to the Allied camp (December 1943).

This and other attempts to secure Romania’s change of allegiance foundered on the Allies' unwavering demand for Romania’s unconditional surrender, which the government of Maresal al România Ion Antonescu saw as being tantamount to a Soviet take-over of his country.

The three agents parachuted into Romania in 1943 were Lieutenant Colonel Alfred Gardyne de Chastelain, experienced SOE officer, as the leader, Captain Ivor Porter and Captain Silviu Meţianu, a Romanian who had emigrated to the UK. The operation’s two objectives were, firstly, to persuade Romanian politicians, especially Iuliu Maniu, the leader of the National Peasants' Party, to negotiate an armistice with the Allied powers and, secondly, in the event that the three-man party was captured by authorities loyal to the Antonescu government, to convince the Romanian secret service during the inevitable interrogation that the Allies were preparing to land in the Balkans and thereby prompt a reinforcement of German strength in the south-east of the European theatre to the detriment of their strength in Normandy.

During the night of 22/23 December 1943 the three agents were parachuted into thick fog and some distance away from the target. They were captured by Romanian gendarmerie almost immediately in the area of Plosca. They were held as well-treated prisoners of war at the gendarmerie headquarters in Bucharest. Prime Minister Winston Churchill promptly sent a message to Antonescu warning him that should the British prisoners fall into German hands that he would be held personally responsible. Churchill had been told that de Chastelain had information which in German hands could change the outcome of the war.

On 23 August 1944 the young King Mihai I of Romania carried out his well prepared coup d'état which took Adolf Hitler completely by surprise, and Romania then changed sides. The British prisoners were released and that evening the king arranged for de Chastelain to fly to Istanbul, whence he could travel to Cairo and then London to report. Meţianu stayed on for a time and then returned to England. Porter remained to maintain a radio link with SOE headquarters until the British mission arrived in the country.