Beginning with the Second Anglo-Afghan War of 1878, the British Army began adopting light khaki uniforms for Tropical service that was first introduced in 1848 with the Corps of Guides in India. This innovation arose from experience fighting irregular forces in India, for example on the Indian North-West Frontier and during the Indian Mutiny, and in Africa during the Anglo-Zulu War, as well as the invention of smokeless gunpowder and the increasing effectiveness and usage of rifles. In 1902 a darker shade of "Service Dress" (SD) was adopted for field and ordinary use in Britain itself. The scarlet, blue and rifle green uniforms were retained for wear as full dress on parade and "walking-out dress" when off duty and out of barracks. As worn between 1902 and 1914 by all non-commissioned ranks, walking-out dress was essentially the same as review order, except that a peaked cap or glengarry was worn instead of the full dress headdress and overalls (strapped trousers) were substituted for cavalry breeches.