from other units), thus gradually depleting their total capabilities. Faced with the threat of losing military capability, initiating the process of technical modernization became a necessity. In 2006, many aging weapons and equipment were decommissioned from combat service by the Air Force. This presented an opportunity to use the released funds to the modernization of various items of aviation and anti-aircraft artillery weapons and equipment, radio communication equipment, and flight maintenance equipment, as well as an improvement of Air Force personnel training. In 2011 International Institute for Strategic Studies estimates that Ukraine's Air Force includes one Sukhoi Su-24M regiment, 5 regiments with Mikoyan MiG-29s and Sukhoi Su-27, one regiment with Sukhoi Su-25, two squadrons with Sukhoi Su-24MR, three transport regiments, some support helicopter squadrons, one helicopter training regiment, and some air training squadrons with L-39 Albatros. The IISS said they were grouped into the 5th and 14th Aviation Corps, the 35th Aviation Group, which is a multi-role rapid reaction formation, and a training aviation command. The IISS assesses the overall force size as 817 aircraft of all types and 43,100 personnel. The aviation corps had actually be reorganised into regional air commands in about 2004. Russian sources list three aviation groups (West, South, and Center). The automated systems of collection, processing and transmission of radio information have been adopted as a component part of the Automated Command and Control System for aviation and air defense. Operational service testing of the circular surveillance radar station has also been completed. Prototypes of high-precision weapons systems, electronic warfare devices, and navigation equipment have been created and developed for state testing. Role in the 2014 Russian invasion of Ukraine Following the Revolution of Dignity and subsequent March 2014 Russian annexation of Crimea and the following violence and insurgency in east Ukraine, Ukraine tried to increase its defence spending and capabilities - with returning equipment to service being a key part of the spending drive. During the 2014 Russian invasion of Crimea the air force did not fight but lost several aircraft to Russia; most were returned to Ukraine. The air force has taken part in the conflict against the 2014 insurgency in Donbas. During this conflict it has lost several planes and helicopters. Wall Street Journal published USA embassy in Kyiv report that Ukraine lost 19 planes and helicopters in the period 22 April - 22 July 2014. According to an unverified October 2015