"American troops have not only occupied Ulster but are arriving in increasing numbers in England"

This quote by John Amery is describing the presence of American soldiers in the United Kingdom throughout World War II. Amery is recommending that American troops have actually not just been stationed in Ulster, which is a region in Northern Ireland, however are likewise getting here in England in increasing numbers. This is likely a referral to the accumulation of American forces in the UK in preparation for the D-Day landings in 1944. The presence of American troops in the UK suggested the strong alliance between the 2 countries and the commitment of the United States to the war effort. The quote also reflects the importance of the UK as a tactical base for the Allies in the war.