The material for the book “Aircraft in Warfare” was originally published in “Engineering” from September to December 1914. It subsequently appeared in book form in 1916. Lanchester at his own expense gave away 1,000 copies to members of the armed forces. The book is best known for Lanchester’s explanation of the N² Law, which is a mathematical theory of the concentration of fighting forces on an enemy and the expected result. It is in fact an early essay in operational research. Most of the letters (LAN/1/3/1 to LAN/1/3/16) are from naval officers who received copies from Lanchester.