Wing Commander Abhinandan Varthaman today led a formation of the IAF's MiG-21 Bison on Indian Air Force Day celebrations over Hindon Air Base near Delhi. The MiG-21 Bison is an upgraded version of the Soviet-era fighter jet. Wing Commander Varthaman had shot down a Pakistani F-16 in February before his aircraft was downed by enemy fire. Air Chief Marshal RKS Bhadauria today said the Indian Air Force (IAF) needs to be alert at all times amid the "present security environment in the neighbourhood". Addressing IAF personnel and their families on the 87th birth anniversary of the Air Force, he said, "All Air Warriors should serve with great integrity at all times". The day is significant for another reason - Defence Minister Rajnath Singh will take delivery of India's newest multirole fighter jet Rafale in France today. Army Chief General Bipin Rawat attended the event.