In October 1939, a month after the outbreak of the
Second World War, Armstrong, now a
major, went to France with the 1st Battalion, East Surrey Regiment, before taking command of the 1/6th Battalion in April 1940 as a temporary
lieutenant colonel. Evacuated from
Dunkirk a month later, he remained in command of the battalion until April 1942. In April 1942 he was posted to command the 70th (Young Soldiers) Battalion, and later 1st Battalion, the
Duke of Wellington's Regiment which, in early 1943 he took to
North Africa. According to some sources, he was carefully selected for this mission because of his lack of political contacts or skill. Together with members of his mission, Armstrong parachuted into Yugoslavia at the end of September 1943. Before he was dispatched to Chetnik headquarters, a previous member of British mission with the Chetniks,
Colonel Bailey, advised him that the Chetniks were angry and that Mihailović "won't hear of British anymore". The United Kingdom had provided substantial supplies to Yugoslav Communist forces who opposed the Chetniks, while the
BBC repeatedly gave the Communist forces credit for the anti-Axis actions of Chetniks, especially during September and October 1943. For example, when Chetniks attacked the German garrison in
Prijepolje on 11 September, killed 200 German soldiers and captured the town, the
BBC credited
Tito's Communist Partisans with the victory. Armstrong and Seitz took part in the Chetnik action against Axis controlled units protecting the railway bridge over
Drina in
Višegrad. In this attack about 2,500 Chetniks killed about 350 Ustaše and German soldiers and captured a lot of ammunition and arms. Before the Chetniks stormed into Višegrad, they first destroyed four smaller bridges in
Mokra Gora. British media, including the
BBC, credited Yugoslav Communist Partisans for this successful action by the Chetniks. In November 1943 the Chetniks attacked Axis positions at
Nova Varoš and Kalna, and both actions were again attributed to Communists by the BBC. Archival evidence, published in 1980 for the first time, confirms that some actions against Axis carried by Mihailović and his Chetniks with Armstrong were mistakenly credited to
Tito and his Communist forces. Armstrong sent an angry protest to the BBC insisting on the publication of correct information, to no avail. Some authors blame the persistent misreporting of BBC and attribution of successful Chetnik anti-Axis actions to Communists on a supposed strong network of Soviet spies in the BBC and the British
Ministry of Information. This misreporting changed British public opinion and even influenced some high-ranking officials. But
Churchill's reason was the evidence of
Ultra decrypts from the Government Code and Cipher School in
Bletchley Park (which he read; they were secret until the 1970s) that Tito's Partisans were a
"much more effective and reliable ally in the war against Germany"; see
Yugoslavia and the Allies.
Tensions between American and British mission Almost as soon as he reached Chetnik headquarters, the relation of British mission toward Mihailović significantly deteriorated and tensions between American and British mission began to develop,
Chetniks ignore Armstrong's orders to destroy bridges Armstrong inherited his predecessor’s (Colonel Bailey) task to convince Mihailovic to increase his anti-Axis activities without providing him with adequate supplies. Armstrong confirmed that Colonel Bailey insisted that Chetniks should not disarm Italians in the valley of river
Lim and to avoid conflict with
Partisans with final consequence that the Chetniks were forced to leave this valley. Until December 1943 the British army delivered only 30 tons of arms to Chetniks and 18,000 tons to the Communist Partisans, who used many British arms to attack Chetniks. Armstrong refused to participate in the
Ba Congress held between 25 and 28 January 1944 because he was dissatisfied with the refusal of the Chetniks to follow British requests to perform two sabotages against the Germans. Armstrong insisted that Chetniks should destroy bridges over river
Morava and river
Ibar near Raška as condition for his participation at the Congress. Leaving Yugoslavia, Armstrong returned to England and, in June 1944, took command of the British Airborne Liaison Unit to the
Polish Parachute Brigade. He remained in the UK for the remainder of the war. == 1945 and after ==