Sligo county is in the Republic of Ireland. Sligo town where the first photo was taken is on the west coast of Ireland. The photographer may be listed in old trade books giving you a clue to the date. Have no ideas about Irish military history.
The other photograph is taken in Aldershot. Could this be Aldershot, Hampshire, England - home of the British Army? My grandfather was in the Royal Army Medical Corps and was stationed at Aldershot for a time - it is a huge garrison town. I think his first stint there was in 1912 before WWI. Again, the name of the photographer will be listed in trade books so you may be able to pin down the date again.