In 2014, Russian aerospace expert Piotr Butowski estimated there were seven squadrons of Tu-22Ms in service, each with approximately 10 aircraft, stationed at three airbases; 40 at Belaya airbase in southeastern Siberia, 28 at Shaykovka airbase southwest of Moscow, and 10 at Dyagilevo airbase in Ryazan southeast of Moscow which serves as the training unit for the bomber. With the deletion of the aircraft's in-flight refueling capability due to the START I treaty, the Tu-22M's internal fuel capacity limits its operational range (combat radius unrefueled: 4,000–5,000 km (DIA), 3,360–3,960 km (CIA) estimate) from its home bases to only around Russia's immediate sphere of influence.