With the initial investment of £4,200, the new trial force of the Thames River Police began with about 50 men charged with policing 33,000 workers in the river trades, of whom Colquhoun claimed 11,000 were known criminals and "on the game." The force was a success after its first year, and his men had "established their worth by saving £122,000 worth of cargo and by the rescuing of several lives." Word of this success spread quickly, and the government passed the Marine Police Bill on 28 July 1800, transforming it from a private to public police agency; now the oldest police force in the world. Colquhoun published a book on the experiment, The Commerce and Policing of the River Thames. It found receptive audiences far outside London, and inspired similar forces in other cities, notably, New York City, Dublin, and Sydney.

What was the initial size of the Thames River Police force?