Pakistan's minorities comprise 3% of Pakistan's population.
By virtue of lack of interest in the profession of the arms, most minorities do not take it up. However given the demographics of the population, Pakistan has had its share of non-Muslims throughout the decades. There is nothing to prove here for Pakistan. If the minorities opt for the Armed Forces, the doors are open, have always been and will always remain that way.
Of the minorities, Christians are the most widely represented in all three arms. Hindus and Sikhs do not join in numbers because of the ideological issues and Pakistan's relations with India. Parsis like the Christians have had a presence in the Armed forces but based on what I have seen, most Parsis who have served have opted for the Army.
Sprinkling of Hindu officers also exist. My own assertion is that most opt for Navy since the proximity of the service's bases around Karachi where the majority of the Hindu population in Pakistan resides but of those who serve, most are in the non-commissioned ranks.
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Obviously the minorities are being encouraged to join in greater numbers and this is a good thing for our national cohesion. Service in the armed forces allows upward mobility to the minorities that are not well off, an exception to the case being the Parsis and Sikhs in Pakistan as they are relatively well off compared to the other minorities, so hopefully this trend will continue to increase.