In Hindi, Marathi, Punjabi, and other Indian languages the word "Kaptaan" was a common mispronunciation for the military rank of Captain from the English language. It's strange that this should be so —- for today's generation of Indians would pronounce Captain as either "Cap-tin" or "Cape-ton". It is not well-known even to students of Indian History that English military ranks were actually derived from Old French and Latin. They came into the Indian languages, not through English but through the original French —- thus "Kaptaan" is in fact the Indian version of the original French word Capitaine.
Similarly the word "Jarnal / Jarnail" are mispronunciations of the old French Generalle and not the English General. "Karnal / Karnail" is from the French Coronel and not the English Colonel. So too "Kumedan" is the old Indian version of the French Commandante. And finally "Paltan" though ostensibly tallying with the English Platoon, is actually derived from the original French Peloton.
Now we know that the British Raj in India grew and perished in a period of under 200 years (1757-1947) and that the British Indian Army was created in this time period. So when and how did French military ranks come into use in the Indian languages?
In fact before the British Empire existed and down at least to 1800 when it was in the midst of forming, French military officers led and organized the armies of Indian Kings —- from the Kingdom of Mysore in the very south of India up to the Kingdom of Punjab in the northwest.
The first to attain fame was Marquis de Bussy who trained the army of the Muslim Kingdom of Hyderabad in southern India —- the infantrymen for this army were local Hindu Telegus. A section of this army, under the native commander Ibrahim Khan Gardi (commandant de la guard), joined the services of the neighboring Maratha Empire and fought with distinction in the Third Battle of Panipat (1761). Armed with French-made Fusils the Telegu soldiers repulsed the advancing army of Ahmad Shah Abdali as long as they had ammunition.
Other noted officers were Rene Madec and Walter Reinhardt Le Sombre —- both of them emerged in North India alternatively serving kingdoms like Bharatpur, Dholpur and Jaipur but ultimately joining the shadowy Mughal Emperor and carving out their own personal estates in his service. While Madec returned home to France with his accumulated wealth, Le Sombre settled down in his estate of Sardhana and married and converted (to Christianity) a Kashmiri dancing girl —- known to history as Begam Samru (here another French word Sombre, was pronounced in the Indian languages as Samru).
The most remarkable Frenchman in this period was Le Borgne de Boigne —- he entered the services of the Maratha chieftain Mahadji Sindhia and helped him win many famous victories in North India (Battles of Agra, Patan, and Merta). Sindhia promoted him to the rank of "Jarnal" when he raised an entire army corps of Purbias and Ruhelas for his master. He was also noted for his civility, personal honesty, and realistic appraisal of the British power.
His successor Cuillier Perron, a particularly dishonest officer, secretly transferred his accumulated hoards to English banks for safety. At that time he was constantly urging his Indian masters to fight the same English! But when the time came for that fight (1803, the Second Anglo-Maratha War) Perron led his personal bodyguard across the River Yamuna into British territory, then bribed the boatmen to prevent the rest of the army from crossing over, while he obtained safe passage from the British back home to France.
The other European officers at Aligarh, Agra, and Delhi, were also in secret communications with the advancing British. They had all planned to desert to the English at the first opportunity and return to Europe with their accumulated wealth. But here the heroic Indian soldiers; Purbias, Marathas and Ruhelas, put their treacherous European commanders in prison and fought gallantly against the British. They were defeated, the units were disbanded, and many of these able-bodied men joined their Purbia brethren under British service.
Thus ended the saga of French-dominated armies in India leaving behind only quaint words like Kaptaan as a reminder of that age!