John is a permanent member of the Irish Naval Service. In 2019, John spent 128 days at sea on board an Irish naval vessel. In 2020, John spent 73 days at sea on board an Irish naval vessel.
John can claim this tax credit for 2020 as he spent at least 80 days at sea in 2019. However, as John spent less than 80 days at sea in 2020, he cannot claim the credit for 2021.