No. 2 - Baltimore, Maryland, USA to Hanau Am Main, Germany

No date, but can be dated to between 17 May, 1915 when British Examination of US transit mail was started and 06 April, 1917 when the US declared war on Germany. The British detained this letter and didn't release it until July 1919, long after the war ended on 11 November, 1918.

The British didn't suspend or detain all mail, between its enemies and the USA, during this period, as they had no desire to antagonize the USA and provide it with more reasons to maintain its neutrality.