In early WW2, how much of the merchant marine was American?

Question

WW2, before the US entered, ran from 1939 Sep 01 to 1941 Dec 07. During this time, a lot of merchant vessels sailed in convoy to Britain.

I am wondering, of all the people who crewed those vessels, how many were American, versus how many were Canadian or British.

Note, I'm not asking for a death toll. I'm asking for a composition of them all.

Answer 1

Question: In early WW2, how much of the merchant marine was American?

Short Answer:

Sept 1939, The United States had 19% of the merchant ships and 27% of the tonnage relative to the British Empire, US, and France.

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Detailed Answer

For the purposes of this question WWII started in Europe, Sept 1939 when Germany invaded Poland, and Britain and France, (and Canada) declared war on Germany.

Percentages are based upon Britain, and British Commonwealth being measured independently. Canada which had no merchant navy when they declared war on Germany Sept 10, 1939 (See Be low), is included because it is mentioned in the question. Percentages are based upon the set of Britain, USA, Commonwealth, and France being the total set. Raw numbers are given be low the percentages.

The outbreak of World War II, Sept 1939.

                                   Ships                          Tonage
         UK                          54%                            54%
         US                          19%                            27%
         Common Wealth               18%                            9%
         France                      10%                            9%
         Canada                       0                             0

Source: WWII Data Book

Countries with over a million tons of merchant shipping on the outbreak of World War II.

          UK                       6722 ships               17,891,134 tons
          USA                      2345 ships               8,909,892 tons
          Japan                    1609 ships               5,996,607 tons
          Norway                   1987 ships               4,833,813 tons
          Germany                  2459 ships               4,482,662 tons
          Italy                    1227 ships               3,424,804 tons
          British Commonwealth*    2255 ships               3,110,791 tons
          Netherlands              1523 ships,              2,969,578 tons
          France                   1231 ships,              2,933,933 tons
          Greece                   607 ships,              1,780,666 tons
          Denmark                  705 ships,              1,174,944 tons

• British Commonwealth excludes UK which is measured independely, Soviet Union didn't meet the minimum requirement of 1 million tons capacity to be included in these numbers,

Canadian Merchant Navy: History
With regards to Canada specifically, Canada had no merchant fleet when WWII broke out. Canada had a small "informal" merchant navy built for WWI, but by 1930 it had disappeared. At the beginning of WWII, "within hours of declaring war" September 10, 1939 Canada began rebuilding the Canadian merchant fleet from the ground up. During WWII the Canadian merchant fleet played an important role in the Battle of the Atlantic "bolstering the allies’ merchant fleet due to high losses in the British Merchant Navy."

Answer 2

According to: http://armed-guard.com/about-mm.html

Prior to the beginning of World War II there about 55,000 civilian sailors employed in the U.S. merchant marine. This number increased to as many as 250,000 men who served in the U.S. merchant marine by the end of the war. A pre-war merchant fleet of 1,340 cargo ships and tankers expanded to at least 4,221 U.S. merchant ships by the end of World War II.