The U.S. was initially prevented by law, the Neutrality Act, from arming its merchant vessels, including transport ships, even though some U.S. merchant vessels were attacked and sunk, beginning as early as November 1940. The U.S. eventually amended the Neutrality Act in November 1941 and began the task of arming its merchant vessels, even before the U.S. joined World War II. But it took time to arm vessels and train and deploy Armed Guard units on the vessels. Training of Armed Guard sailors and officers began in April 1941, and the first Armed Guard crew was placed on SS DUNBOYNE, a cargo vessel, on December 2, 1941.
U.S. merchant vessels carrying war supplies to Britain began sailing in eastbound convoys in the North Atlantic in mid-September 1941. While the U.S. vessels presumably would have been unarmed, the convoys had warship escorts and any accompanying British merchant vessels in the convoy were themselves armed. U.S. Navy and Coast Guard warships began convoy escort duty in the North Atlantic also in September 1941.
I have found information that transport ships carried passengers (although not necessarily military personnel) in both directions across the Atlantic prior to December 7, 1941, either in convoy or unescorted. If the vessels were in convoy and were British, they were armed with British gunners, plus the convoys had warship escorts. In other cases U.S. transports sailed eastbound or westbound across the Atlantic, for example to carry German and Italian diplomats and their families from the U.S. to Europe, or to take U.S. diplomats removed from their posts in Germany, German-occupied countries and Italy from Europe to the U.S. These transports were either high-speed passenger vessels (able to outrun German U-boats) or had their safe passage guaranteed, but presumably were unarmed.
In other cases prior to December 7, 1941, U.S. troopships transported U.S. troops to such locations as Wake Island, Samoa, Greenland and Iceland to construct military facilities or to man such facilities. These transports were escorted by U.S. warships.
Additionally there was at least one case of a convoy of British troop transports with 20,000 British troops aboard, as convoy CT-5, that sailed from Scotland to Halifax. These transports subsequently sailed from Halifax to the Middle East. The British ships would have had their own on-board gunners and there would have been escorting warships, either British or U.S.
I have not found information about any troop transports operating between New York or Halifax to Liverpool prior to December 7, 1941.
Ron Carlson, Webmaster
Armed Guard/Merchant Marine website