It may appear something which is unlikely and preposterous, yet a gleaning of the history of the Indian army brings out the fact that Sikhs are discriminated against right from the time of Jwaharlal Nehru. The discrimination has been for the post of the army chief, and it it is more by rule then exception.
The Sikhs after the Anglo-Sikh wars (1846-49), became the lynchpin of the British Indian army. They constituted a strength of 33% of the army, though having only a 2% share of the population of India. When India became "free" in 1947, the Indian army had a strength of about 500,000 and the strength of Sikhs in the officer cadre was a neat 33%.
Jwaharlal Nehru is known to have had some phobia about Sikhs. One cannot however prove anything , but 2 facts stand out. He refused to accede to a Punjabi speaking state, despite he himself having formulated the concept of division of India on linguist lines. Secondly he discriminated against Sikhs in matters of appointments to senior and crucial appointments. Thus it was no surprise
that when the time came to choose the Army Chief in 1951, the senior Sikh general Lt Gen Kulwant Singh was superseded by L Gen Cariappa. In any case Cariappa was beholden to Nehru for his promotion and sat passively when the first demotions in perks and privileges were applied in for the army.
During the 1965 war with Pakistan the man who saved India , army commander western command Lt Gen Harbaksh Singh was to be appointed the Army Chief (COAS) in 1969. Despite a press release, he was overnight superseded by Maneckshaw. Harbaksh was a Sikh.
The Rajiv Gandhi era were the worst for Sikh generals. For 6 years the only command given to Sikhs was Southern Command and a string of Sikhs were sent to this comparative obscure command. No Sikh general was given command of any strategic command like Western Command.
Thus no Sikh became army chief for 4 decades, despite having 33% strength in highest echelons of the army. This state of affairs only changed when the Congress party was defeated and BJP came to power and JJ Singh became first Sikh army chief.