Indians in France

A postcard of some Indians fighting for the British in France, 1914.
https://i.servimg.com/u/f22/12/22/09/10/324_0010.jpg
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When I see an Indian soldier in a tarboosh, "Madras Sappers and Miners" pops into my head, but it might be "Bombay Sappers and Miners," or something. Memory's hazy here.

Your memory was correct mconrad. The tall fez-like headdress (sometimes described as a peakless survival of the old shako) was the distinction of of the Madras Sappers and Miners from at least the 1890s. Simkin shows it as blue with a narrow red turban around the lower edge. With service dress a plain khaki version was worn, as in the photo. It was still being worn on active service in Burma as late as 1945, which indicates it must have been practical enough for modern warfare. The modern Madras Sappers still wear what is variously called a dupta or doopta as part of their parade dress.

This headdress was unique to the Madras Sappers and Miners - the other corps (Bengal and Bombay) wore the usual turbans.