At the onset of Great Patriotic War on 22 June 1941, 425 Yak-1 were built, although many of these were en route or still disassembled. Just 92 machines were fully operational in the Western Military Districts – but most were lost in the very first days of the war. Yak-1 was designed with the goal of providing direct coverage of the Il-2 attack planes from enemy fighters. Thus, most of the air combat took place below 4,000 m (13,123 ft), at low altitudes, where Yak-1 performed the best. The Yak-1 proved to have a significant advantage over its Soviet competitors. A full circle turn took just 17 seconds in the Yak-1M. The MiG-3, which had the best high-altitude performance, did poorly at low and medium altitudes, and its light armament made it unsuitable even for ground attack. The LaGG-3 experienced a significant degradation in performance (as much as 100 km/h/62 mph on some aircraft) compared to its prototypes due to the manufacturer’s inexperience with its special wooden construction, which suffered from warping and rotting when exposed to the elements. The Yak-1’s plywood covering also suffered from the weather, but the steel frame kept the aircraft largely intact.
The aircraft’s major problem early in deployment was fuel leaks caused by failure of spot-welded fuel tanks from vibration. Also troublesome was the fact that the canopy could not be opened under certain conditions in earlier models, potentially trapping the pilot in a falling aircraft. As the result, some pilots had the sliding portion of the canopy removed altogether. The first 1,000 Yak-1 had no radios at all. Installation of radio equipment became common by spring 1942 and obligatory by August 1942. But Soviet radios were notoriously unreliable and short-ranged, so they were frequently removed to save weight.
Like most early carburetor-equipped engines, the M-105 could not tolerate negative G forces, which starved it of fuel. Moreover, they suffered breakdowns of magnetos and speed governors, and emitted oil from the reduction shaft.
The Yak-1 was better than Bf 109E but inferior to Bf 109F – its main opponent – in rate of climb at all altitudes. And although it could complete a circle at the same speed (20–21 seconds at 1,000 meters) as a Bf 109, its lack of agility made dogfights difficult, demanding high levels of concentration. In comparison, a Bf 109, with its automatic flaps, had a lower stall speed and was more stable in sharp turns and vertical aerobatic figures. A simulated combat between a Yak (with M-105PF engine) and a Bf 109F revealed that the Messerschmitt had only marginally superior manoeuvrability at 1,000 meters (3,300 ft), though the German fighter could gain substantial advantage over the Yak-1 within four or five nose-to-tail turns. At 3,000 meters (9,800 ft) the capabilities of the two fighters were nearly equal, combat essentially reduced to head-on attacks. At altitudes over 5,000 meters ( 16,400 ft) the Yak was more manoeuvrable. The engine’s nominal speed at low altitudes was increased to 2,550 rpm and the superiority of the Bf 109F at these altitudes was reduced.
Its armament would be considered too light by Western standards, but was perfectly typical of Soviet aircraft, the pilots of which preferred a few guns grouped on the centerline to improve accuracy and lower weight. Wing guns were rarely used on Soviet fighters, and when they were they were often removed (as they were from US-supplied Bell P-39 Airacobras). Avoiding wing guns lowered weight and demonstrably improved roll rates (the same was true with the Bf 109F). The US and Britain considered heavy armament and high performance necessary even at the cost of reduced agility, while the Soviets relied on the marksmanship of their pilots coupled with agile aircraft. Even with the Yak-1’s light armament, to reduce weight, modifications were made both on front line and on about thirty production aircraft: the 7,62 mm ShKAS machine guns were removed, retaining only the single ShVAK cannon. Nevertheless, those lighter aircraft were popular with experienced pilots, for whom the reduction in armament was acceptable, and combat experience in November 1942 showed a much improved kill-to-loss ratio. Also, in the autumn of 1942 the Yak-1B appeared with the more powerful M-105P engine and a single 12,7 mm UBS machine gun instead of the two ShKAS. Although this did not increase the total weight of fire by much, the UBS machine gun was much more effective than the two 7,62 mm ShKAS. Moreover, the simple VV ring sight replaced the PBP gun-sight, because of the very poor quality of the lenses of the latter. The Yak-1 had a light tail and it was easy to tip over and to hit the ground with the propeller. Often technicians had to keep the tail down and that could lead to accidents, with aircraft taking off with technicians still on the rear fuselage. This was true of other aircraft as well; an almost identical complaint was made about the Supermarine Spitfires in Soviet use, although in that case it was compounded by a very narrow landing gear track.
Nonetheless, the Yak-1 was well liked by its pilots. For Soviet pilot Nikolai G. Golodnikov, overall, in its tactical and technical characteristic, the Yak-1B was comparable to the Messerschmitt Bf 109G at low to mid, but vastly inferior in top speed and high altitude performance. French Normandie-Niemen squadron selected the primitive model Yak-1M (that had a cut-down fuselage to allow all-round vision) when it was formed, in March 1943. Twenty-four of these aircraft were sent to the elite all-female 586 IAP whose pilots included the world’s only female aces: Katya Budanova, with 11, and Lydia Litvyak (11 plus three shared). Litvyak, the most famous fighter pilot woman of all time, flew Yak-1 “Yellow 44”, with aerial mast, at first in 296.IAP and then with 73.Gv.IAP, until her death in combat, on 1 August 1943. Another famous ace who flew the Yak-1 was Mikhail Baranov, who scored all his 24 victories on it, including five on a day (four Bf 109s and one Ju 87, on 6 August 1942). Yak-1s were also the first type operated by the 1 Pułk Lotnictwa Myśliwskiego “Warszawa” (“1st Polish Fighter Regiment ‘Warsaw'”).
The importance of this type in World War II is often underestimated. Soviet naming conventions obscure the fact that the Yak-1 and its successors — the Yak-7, Yak-9 and Yak-3 — are essentially the same design, comparable to the numerous Spitfire or Bf 109 variants. Were the Yaks considered as one type, the 37,000 built would constitute the most produced fighter in history. That total would also make the Yak one of the most prolific aircraft in history, roughly equal to the best known Soviet ground attack type of World War II, the IL-2 Shturmovik. But losses were proportionally high, in fact the highest of all fighters type in service in USSR: in 1941-1945 VVS KA lost 3,336 Yak-1s; 325 in 1941, 1,301 the following year, 1,056 in 1943, 575 in 1944 and 79 in 1945