India is a pretty huge country, I think it didn't have huge naval power or strong army, ut still it had several kingdoms and rulers. How did they all bow don to the British without any notable resistance?
I am curious as to where you heard that the subjection of India was quick and peaceful, as the process was neither.
The English Traders that entered the Indian Ocean at the turn of the 17th century had to contend with other European powers such as the Dutch, the Portuguese and later, the French. Needless to say there were many battles between the European powers in order to secure the lucrative Indian trading outposts. A major series of conflicts, which happened between 1744 and 1763, known as the Carnatic Wars really cemented the East India Company as a dominant player in India. The decisive battle occurred in 1757 between the East India Company and the French supported Nawab of Bengal; the triumph of the East India Company allowed them to assume control of the rich region of Bengal and cripple French ambitions of an Indian empire.
The British also had to contend with local powers such as the Marathas, the Sikhs and the Kingdom of Mysore (made famous for their rocket artillery) who all put up stiff and occasionally successful military resistance.
Even after subduing the local powers, there was at least one major military attempt at overthrowing British power - the Sepoy Rebellion of 1857. As the name implies, the native troops employed by the East India Company rose up in rebellion and they were supported by some local rulers. The rebellion was crushed by British troops by 1858 and the episode resulted in the British government taking control of India from the East India Company.
That is a rudimentary summary of the numerous conflicts the English had to face in order to control India. As mentioned, the conquest and holding of India was neither quick nor bloodless.
Edit: Modified the summary of the Sepoy Rebellion to better clarify the extent of support the sepoys had. As pointed out below many states remained neutral (such as Mysore) or actively supported the British (such as the Sikhs). Of course, the rulers that achieved fame were the ones who took up arms against the British such as the Rani of Jhansi.
Not sure where you got the idea that the indian subcontinent was not a martial state. The region has a history of strong military states that competed for authority. Typically the simplest reason given for how the British were able to overcome them was by using their divisions against them. (divide and conquer)
http://en.wikipedia.org/wiki/Military_history_of_India#The_Medieval_era