Since January 1912, Vessels Landing Or Embarking Bullion, Spice, Or Mails Only, Are Included In Returns As Vessels With Cargoes. They Were Previously Considered Vessels In Ballast. Data Exclude The Irish Free State From April 1923 On. Source: Board Of Trade, Statistical Office, "Accounts Relating To Trade And Navigation".
This NBER data series m03024 appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: m03024
Release: NBER Macrohistory Database
National Bureau of Economic Research, Tonnage Cleared, British and Foreign for Great Britain [M03024GBM583NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M03024GBM583NNBR/, July 1, 2015.