Convert from twain to military pace [double time]

Unit Definition (twain)
The twain is an old word for the number two, derived from the Anglo-Saxon twegen. The American author Samuel Clemens (1835-1910), who had been a riverboat pilot on the Mississippi in his youth, took his literary name from a traditional riverboat phrase "mark twain", meaning "exactly two" fathoms of water. This was the minimum depth needed for the boats to operate safely without running aground.

Unit Definition (military pace [double time])
The length of a single step in marching (taken to be 30 inches for quick time or 36 inches for double time).