Mr Singh, 98, the only officer of the IAF to be promoted to five-star rank, was admitted to the Army’s Research and Referral hospital this morning.
Defence Minister Nirmala Sitharaman and IAF chief BS Dhanoa visited the hospital. “His condition is critical,” official sources said.
He was admitted to the hospital after he complained of uneasiness.
An icon of the Indian military history, Mr Singh had led a young IAF into the war in 1965 when he was hardly 44 years of age.
In 1965, when Pakistan had launched its Operation Grand Slam with an armoured thrust targeted at the vital town of Akhnoor, Singh led the Indian Air Force through the war with courage, determination and professional skill.
He inspired the IAF to victory, despite the constraints imposed on a full-scale use of air force combat power.