To mark St Patrick's Day the Irish Navy has brought its patrol ship Le Roisin to London. It is moored alongside HMS Belfast.
The Irish ship is open to the public this week.
Le Roisin P51 entered service in 1999 and is best known for her dramatic rescue of the Canadian Forces submarine CHICOUTIMI off the North Western Coast of Ireland on 5 October 2004 when she was seriously damaged in the rescue mission.
HMS Belfast was launched on St Patrick's Day in 1938.
"Le Roisin is a fantastic example of today's modern Irish Naval ship," says Brad King, director of HMS Belfast.
"A first-class vessel of her kind, she incredibly sleek, fast and tough because she was built specifically for North Atlantic winter operations and to endure some of the most dangerous sea conditions in the world.
"We are thrilled to have her moored alongside and we hope that she will attract some visitors during her stay."
Tower Bridge will lift at 7am on Thursday morning when Le Roisin departs for Ireland.