 War between Britain and Persia broke out in 1856 and the 64th, together with the 20th Bombay Native Infantry, formed the 1st Brigade in the expeditionary force assembled for the campaign.Landing in Persia in late November, the regiment took place in battles at Reshire and Bushire.In 1857 the force advanced inland and defeated the Persian field army at Koosh-Ab on 8 February 1857 while the flank companies were involved in action at Ahwaz.