We report estimates of the fiscal multiplier for interwar Britain based on quarterly data, time-series econometrics, and ‘defense news’. We find that the government expenditure multiplier was in the range 0.3 to 0.8, much lower than previous estimates. The scope for a Keynesian solution to recession was less than is generally supposed. We find that rearmament gave a smaller boost to real GDP than previously claimed. Rearmament may, however, have had a larger impact than a temporary public works program of similar magnitude if private investment anticipated the need to add capacity to cope with future defense spending.