The government on Saturday announced Lt Gen Bipin Rawat as the next Army chief superseding two seniormost Lt Generals, Praveen Bakshi and PM Hariz.
The move has evoked criticism for ignoring long-standing seniority principle in appointing Service chiefs.
Congress and the Left have questioned the appointment of the new army chief by superseding two officers, saying every appointment by the government has become controversial.
The only other time the seniority rule was ignored was in 1983 when the then Prime Minister Indira Gandhi had appointed Lt Gen A S Vaidya as army chief superseding Lt Gen S K Sinha, who resigned in protest.
Earlier in 1972, the Gandhi government side-stepped the very popular Lt General P S Bhagat, one of the handful of Indian Victoria Cross awardees from World War II, who was in line to succeed General (later Field Marshal) Sam Manekshaw.
This was done by giving his junior, General G G Bewoor a year's extension, during which time Bhagat retired. Bewoor, thus, succeeded Manekshaw.
"Government has decided to appoint Lt Gen Bipin Rawat, vice chief of army staff, as the next chief of army staff with effect from afternoon of December 31," the Defence Ministry said in a tweet.
Rawat will replace General Dalbir Singh Suhag who is set to retire at the end of the year.
Congress spokesperson Manish Tewari said that every institution has its own dynamics, hierarchy and seniority which is the overriding dynamic of the armed forces not only in India but everywhere in the world.
"With all due respect to Gen Rawat's professionalism and no personal animus towards anybody, there is a legitimate question that why has that supersession taken place," he said.
Arguing that Eastern Army Commander Lt Gen Praveen Bakshi and Southern Army Command chief Lt Gen P M Hariz are senior to Lt Gen Rawat, Tewari questioned why this supersession has taken place.
He said now the argument the government will give that Congress did supersession in the 80s and, therefore it has the right to do so is a "complete nonsense".
"Every situation has its own context and, therefore nothing can be extrapolated out of context in order to justify a supersession. So, therefore the government needs to answer this legitimate question as to why these senior army commanders were superseded," he said.
"Did the government have anything against them? Was their professionalism in question? What was the reason and I guess the army being a public institution the country deserves those answers," Tewari said.
CPI leader D Raja also questioned the government's move and said appointments have become controversial.
"Appointments in the army have become controversial, the appointments in the judiciary are already controversial, the appointments of CVCs, CBI director and to Central Information Commission, all these top-level appointments are becoming very controversial," he said.
Terming this as "very unfortunate", Raja said it is not inthe interest of democracy and the country.
He said there should be transparency and transparency should go along with integrity and nobody should raise questions. "But now questions are being raised," he added.
Lt Gen Rawat, an infantry soldier, superseded senior most army commander Lt Gen Praveen Bakshi, who headed the Eastern Command and was next in line to be the army chief, besides Southern Command Chief P M Hariz.
Government sources said Lt Gen Rawat was found best suited among the Lt Generals to deal with emerging challenges, including a reorganized and restructured military force in the north, continuing terrorism and proxy war from the west, and the situation in the North-East.
They said Lt Gen Rawat has tremendous hands-on experience of serving in combat areas and at various functional levels in the Indian Army over the last three decades.
He has handled various operational responsibilities in many areas, including along the LoC with Pakistan, the LAC with China and in the North-East.
He is known for his balanced approach towards soldiering, compassion, and connect with civil society. His experience as GOC-in-C Southern Army Command in Mechanised Warfare has been focused towards the western borders, in coordination with the other two services, the sources said.
Defence Ministry sources said the focus was on suitability and merit for the selection of the new Army chief.
They said that Lt Gen Bakshi, an Armoured corps officer, spent most of his career in Jodhpur and had two postings in Kashmir but the positions he was in were not considered field posting.
The sources added that Lt Gen Hariz had no experience in operational areas in terms of counter insurgency or seeing action along the LoC.
With Lt Gen Rawat's sudden promotion as the army chief, the line of succession in the force will get affected.
Rawat was commissioned in the Fifth Battalion of the Eleven Gorkha Rifles in December 1978, from IMA, Dehradun, where he was awarded the 'Sword of Honour'.
The General Officer has vast experience in high altitude warfare and counter insurgency operations.
He commanded an Infantry battalion along the Line of Actual Control in the Eastern sector, a Rashtriya Rifles sector and an Infantry Division in the Kashmir Valley. He has tenanted instructional appointments at Indian Military Academy, Dehradun and Army War College, Mhow.
Lt Gen Rawat also held important staff appointments at Directorate General of Military Operations and Military Secretary's Branch at Army Headquarters.
He has been Major General General Staff at HQ Eastern Command. The officer commanded a Multinational Brigade in a Chapter VII mission in the Democratic Republic of Congo (MONUC).
An alumni of Defence Services Staff College, Wellington, the Higher Command and National Defence College Courses, the General Officer, during the span of over 35 years of service in uniform, has been awarded for gallantry and distinguished service.
Prior to taking over as the VCOAS, Lt Gen Rawat was holding the post of the GOC-in-C, Southern Command.
The Indian Air Force, which has also seen supersession in the past, was set for a smooth transition with vice chief of air staff Air Marshal B S Dhanoa, the first in line for the post, named its new chief.
He was commissioned into the fighter stream of the IAF in June 1978. He has served in various squadrons and in the Intelligence Directorate of Air Headquarters.