Analysis of information sources in references of the Wikipedia article "Knot (unit)" in English language version.
The knot is defined as one nautical mile per hour. There is no internationally agreed symbol, but the symbol kn is commonly used.
Since the 1890s or thereabouts, it has been drummed into the young seaman that a knot is a unit of speed, namely, one nautical mile per hour; and that consequently only the uneducated speak of "knots per hour" or "knots an hour". It was therefore inevitable that Kipling's frequent use of this expression should grieve a number of seafaring readers, as the pages of the Kipling Journal testify.
