Q&A: Why two detained trawlers have created such a stormy mood
What is the Voisinage Arrangement? It is a 'gentlemen's agreement' between Ireland and the UK that allows for mutual access to Northern and Republic of Ireland vessels up to six nautical miles off the coast of each.
The reciprocal access dates back to a deal agreed between Seán Lemass and prime minister Terence O'Neill in 1965.
If there's an agreement why were two trawlers impounded this week?
While the agreement has been in place for decades, it was never actually incorporated properly into Irish law. In 2016 four mussel fishermen from Wexford, Waterford, Donegal and Limerick took a legal case claiming they faced financial ruin because of dredging of mussel seed stocks in southern waters by Northern Irish-registered vessels. The Supreme Court issued a judgment which effectively struck down the arrangement.
But can't the navy simply turn a blind eye to Northern Ireland trawlers anyway?
The Sea Fisheries Protection Authority is charged with ensuring fishing zones are respected. The boats were picked up during a routine operation.
Why are there headlines about gunships?
The trawlers were detained by the LÉ Orla, formerly HMS Swift, a British navy vessel. She was purchased by the Irish State in 1988.
The Defence Forces describe it as "designed to move rapidly about the patrol area and to bring her considerable firepower to bear when necessary".
Can't the Government simply pass new legislation?
The Supreme Court noted that the arrangements were a sensible recognition of practice and tradition. As a result of the judgment, the Sea-Fisheries (Amendment) Bill 2017 was published in February 2017. But it got stuck in the Seanad because the Government couldn't muster a majority to support it. Fresh efforts are now being made.
What about Irish-registered boats that go North?
The House of Commons Northern Ireland Affairs Committee has said if something is not done about this by the end of March, Irish fishing vessels will be prevented from going into British waters.
Does Brexit come into this?
Technically no, but there is suspicion among some that Ireland is stalling on legislation so it can be used as a bargaining chip. The fisheries sector is probably the most exposed to a hard Brexit.