The Royal Navy will be joined by allied and merchant vessels in Liverpool to mark the anniversary of the Battle of the Atlantic.
Led by destroyer HMS Defender, the ships are due to arrive on the morning of Friday, May 26, the start of three days of events to mark the 80th anniversary of the fight for control of the Atlantic Ocean during the Second World War.
The Battle of the Atlantic was the longest continuous naval campaign in British history, lasting for the duration of the war from 1939 to 1945.
Commodore Phil Waterhouse, the Navy's Regional Commander for Northern England, said: "This will probably be our final chance to say 'thank you' to that wonderful wartime generation who fought the battle – serving in the ships, in the docks, in the shipyards, in the homes.
"No city is more connected with the Battle of the Atlantic than Liverpool. It felt its effects, suffered the loss of men, suffered under the bombs, waved U-boat hunters off to sea, and celebrated their return.
"So, there can be no more fitting setting for these 80th anniversary commemorations."
Princess Anne will be the guest of honour at the service during an event that will honour the memories of thousands of UK and allied sailors, both military and merchant, who served during the conflict.
After the church service, the Princess Royal will unveil a new Battle of the Atlantic Memorial and a garden of reflection – the first of its kind in the UK.
Cdre Waterhouse added: "It also a chance to remind people that the sea remains the lifeblood of Britain's prosperity – 95% of our trade and 97% of the UK's gas supply comes by sea, mostly through pipelines, while 99% of our data passes through undersea cables.
"The Royal Navy is out there, in home waters and beyond, every day, safeguarding those routes and the shipping using them."