Ninths

London, March 17 (IANS) Photographs clicked by a World War I soldier, who was posted in India and Mesopotamia, show troops having a whale of a time - swimming, riding and visiting the Taj Mahal, a media report said Wednesday.
Private Wally Langrish's photographs paint a picture that is different to the grim images of the trenches and corpses on the front, Daily Express reported.
Langrish was part of the 1/9 cycle battalion of the Hampshire Regiment. He left home in Aldershot in May, 1915, and was posted to India and Mesopotamia before returning home in 1919.
Sixty of his black and white pictures, which have been properly dated and labelled, show troops swimming, riding camels and visiting the Taj Mahal.
'The ninths went to India and Mesopotamia and in 1919 went to Russia and saw a bit of action,' Michael Stephens, curator of the Royal Hampshire Regiment museum, Winchester, was quoted as saying.
The album is expected to fetch 300 pounds at an auction Saturday.

Could you please explain to me what "ninths" mean in this context?

Source : http://in.news.yahoo.com/43/20100317/884/twl-nearly-100-year-old-india-photos-une.html