The 'In the Next War' series of books was published in London by Geoffrey Bles in 1938 and 1939. See here for a discussion.

1938:

• Air Power in the Next War by J. M. Spaight
• Propaganda in the Next War by Sidney Rogerson
• Sea Power in the Next War by Russell Grenfell
• Tanks in the Next War By Eric William Sheppard

1939:

• Gas in the Next War by Henry F. Thuillier
• The Territorial in the Next War by W.E. Green

The following titles were advertised, but apparently never published.

• Infantry in the Next War by E. E. Dorman Smith
• The Civilian in the Next War by Jonathan Griffin