a source of spare parts for other aircraft in the demonstration fleet. Initially, one static and three flyable prototypes (bort no. 901, 902, 904) were built between 2007 and 2009. The third one (bort no. 904) was later destroyed when it crashed into a barrier during its taxi runs. The first contract for 48 production aircraft was signed at the 2009 MAKS Air show in Moscow. In May 2011, Sukhoi delivered the first Su-35S to Akhtubinsk to conduct state joint tests with the Defence Ministry to prepare for operational service. The first of two stages of the trials commenced in August 2011. By March 2012, the two prototypes and four production aircraft were conducting flights to test the type's technical characteristics, which were assessed by the end of that year to have generally complied with requirements. A batch of six production aircraft was handed over in December 2012. In February 2013, five of these at the Gromov Flight Research Institute in Zhukovsky started the second stage of the trials, focusing on the Su-35's weapons and combat maneuverability. Twelve production Su-35Ss were delivered in December 2013, followed by another twelve production aircraft in February 2014, ten of which were handed over to the 23rd Fighter Aviation Regiment stationed in the Far East with the remaining two tasked with carrying out the final phase of state joint tests. The handover marked its official entry into operational service. Several Su-35Ss were later transferred to Lipetsk to further develop combat tactics and to train service personnel. The Russia's Su-35Ss are also permanently based at Besovets air base near the Finnish border, and at Centralnaya Uglovaya air base near Vladivostok. The introduction of the Su-35S into the service with the Russian Air Force is a part of the Russia's state armament programme for 2011–2020 that was formulated following the war with Georgia in 2008 with an aim to significantly increase the number of modern military equipment in the Russian Armed Forces. The aircraft is delivered alongside the Su-30M2 and Su-30SM and the heavier Su-34 strike aircraft. The first two are domestic variants of KnAAPO's Su-30MK2 and Irkut's Su-30MKI two-seat export aircraft. According to reports, the simultaneous acquisition of three fighter derivatives of the original Su-27 was to support the two aircraft manufacturers amidst a slump in export orders. The Su-30M2 serves as a trainer aircraft for the Su-35. The Su-35S attained full operational capability (FOC)