Then-Captain Dyakonov was sent to the
Northwestern Front to fight in the
Winter War in late 1939 and appointed commander of the 60th Separate Volunteer Ski Detachment, formed in the
7th Army and designed to bypass Finnish lines on the
Gulf of Finland. The detachment fought together with the
86th Motor Rifle Division in the battles for the
Koivisto Islands and
Koivisto. Subsequently, Dyakonov led a group of soldiers on a 25-kilometer night march into the rear of the Finnish fortifications defending Tiurinsaari island and attacked elements of the garrison, capturing and holding positions on the island, which enabled the ski detachment to carry out its mission. In the battle they were credited with killing up to 300 Finnish soldiers and capturing elements. His battalion went on to cut the
Vyborg–
Helsinki highway. These actions were described by the writer
Vladimir Stavsky in the eighth issue of the
Krasnoarmeyets magazine for 1940. For his leadership, Dyakonov received the title
Hero of the Soviet Union and was awarded the
Order of Lenin on 21 March. In late February 1940, he took command of the 284th Motor Rifle Regiment of the 86th Rifle Division, but his tenure proved brief as he was wounded in action on 2 March during the battles for Vyborg and evacuated to the rear. After recovering, Dyakonov was appointed commander of the 380th Rifle Regiment of the
117th Rifle Division of the
North Caucasus Military District at
Kamensk-Shakhtinsky on 9 May. In the spring of 1941, he was sent to study at the
Frunze Military Academy. After
Operation Barbarossa began on 22 June, Dyakonov left the academy and in September took command of the 27th Separate Cadet Rifle Brigade. Until November the brigade fought in heavy defensive battles near
Moscow, then was relocated to the
Kalinin Front and fought in the destruction of the German forces around
Lake Seliger, the capture of
Molotitsy and the encirclement of the
Demyansk Pocket. On 29 January then-Colonel Dyakonov took command of the
257th Rifle Division of the
3rd Shock Army, which he led in the
Toropets–Kholm offensive. Its units advanced more than 380 km in fighting from
Ostashkov to
Velikiye Luki, then transitioned to the defensive. In the spring of 1942, the 31st Rifle Brigade and two ski battalions were placed under the control of the division, expanding its defensive line from 40 to 80 km. During the
Battle of Velikiye Luki, the division distinguished itself in the capture of the city and other fortified points, for which it was converted into the
91st Guards Rifle Division on 18 April. Dyakonov rose to deputy commander of the
43rd Army in March 1943 and served in the same role for the
4th Shock Army from 30 June. He took command of the
83rd Rifle Corps of the
39th Army on 20 July, leading it in the
Smolensk and
Dukhovshchina-Demidov offensives. The corps went on to fight as part of the 4th Shock,
6th Guards, and 43rd Armies in attacks towards
Vitebsk, the
Nevel Offensive, and the
Gorodok Offensive, then until early April 1944 defended
Nevel. From April 1944 to March 1945 Dyakonov completed an accelerated course at the
Voroshilov Higher Military Academy, then was sent to the
Far Eastern Front, taking command of the
56th Rifle Corps of the
16th Army on 27 March. During the
Soviet–Japanese War, Dyakonov led the corps in the
invasion of South Sakhalin, in which it played a key role, in cooperation with the
Northern Pacific Flotilla. In difficult conditions of swampy and mountainous terrain, its units broke through Japanese fortified positions of the Koton (Kharamitog) fortified region and rapidly continued on to
Shiritoru,
Ochiai, and
Toyohara. == Postwar ==