On Jan 6th there were the following US warplanes at Shannon:

1. US Air Force C17A Globemaster transport aircraft number 08-8201 landed at about 14.46 pm, coming from Rome with a stop at Ramstein US air base in Germany. It took off again about 16.50 and returned to Ramstein Air Base. 
2. US Air Force C17A Globemaster transport aircraft number 04-4128 landed at about 17.30 pm, coming from Ramstein US air base in Germany. It took off again about 19.30 and returned to Ramstein Air Base. 
3. US Marine Corps Hercules KC130J, mid air refuelling aircraft number 16-6764 landed at about 19.25 pm, coming from Glasgow and Oslo.
4. US Air Force C17A Globemaster transport aircraft number 02-1098 landed at about 19.30 pm, coming from Rome with a stop at Ramstein US air base in Germany. 

That makes 3 large US air force C17 transport aircraft and one US marine Corps mid air refuelling aircraft (probably on a separate mission). What were those 3 C17 doing at Shannon? They are not supposed be on training missions, or intelligence missions, yet it is likely that they were doing both. The were probably flying into Shannon on so-called familiarisation flights, which amount to intelligence gathering. Irish minister for Foreign Affairs Micheal Martin has questions to answer.

Photo shows a US Air Force (05-5153) C-17A Globemaster III. Credit: Bidgee, CC BY-SA 3.0 AU <https://creativecommons.org/licenses/by-sa/3.0/au/deed.en>, via Wikimedia Commons