[2][3] After serving in Afghanistan and in the North-West Frontier Province, the regiment joined the Sindh Expedition, coming under the command of General Sir Charles James Napier, who conquered Sindh in 1843 and sent back to the Governor General the one-word message "Peccavi" – Latin for "I have sinned".

This proved to be a story invented by sixteen-year-old Catherine Winkworth, which her governess sent to Punch magazine, where it was published as a humorous anecdote.

[6] Captain W. Rice of the 25th Bombay Native Infantry, commanding the Goonah Column, wrote from camp at Arone to Sir Robert Napier on 23 December 1858 to report the success of his men, after a moonlight march through dense jungle, in breaking up the camp near Sypoor of rebels led by Feroz Shah, capturing "100 horses, several camels, and many arms", causing the enemy to "flee with the utmost despatch, and seek shelter among the dense foliage, on all sides around their position".

Napier wrote to the Chief of the Staff on Christmas Day of this action "Although they did not lose many men killed, the capture of their horses and property must tend greatly to cripple and break up the party.

[3][8] After the Mutiny, the regiment went on to serve in Hyderabad, Poona, Aurangabad, Mhow, Indore and Dhar, remaining part of the army of the Bombay Presidency until a reorganization of the Indian Army by Lord Kitchener in 1903 (the Kitchener Reforms) gave it the new name; '125th Napier's Rifles'.

[2][3] During the First World War, the regiment fought in both the European and Middle Eastern theatres of the war, from France to Mesopotamia, and participated as part of the Egyptian Expeditionary Force in General Allenby's march to take Jerusalem, getting the better of German and Ottoman opponents.

A Rajput officer of the Indian Army, Amar Singh, who kept a diary in English from 1905 to 1921, paid particular attention to the regiment's wartime role.