The head of Lynn Canal was the main gateway to the Yukon, and the North-West Mounted Police (NWMP) sent a detachment to secure the location for Canada. This was based on Canada's assertion that that location was more than ten marine leagues from the sea, which was part of the 1825 boundary definition. A massive influx of American stampeders through Skagway very quickly forced the Canadian police to retreat. They set up posts on the desolate summits of Chilkoot and White Passes, complete with a mounted Gatling gun at each post. This was still disputed territory, as many Americans believed that the head of Lake Bennett, another north, should be the location of the border. To back up the police in their sovereignty claim, the Canadian government also sent the Yukon Field Force, a 200-man Army unit, to the territory. The soldiers set up camp at Fort Selkirk so that they could be fairly quickly dispatched to deal with problems at either the coastal passes or the 141st meridian west.