The National Memorial Arboretum in the UK has a memorial dedicated to the Merchant Navy. When visiting the scale of it is thought provoking, each tree represents a lost UK ship.
https://www.iwm.org.uk/memorials/item/memorial/13633
> A wood of oak trees representing the 'convoy' of merchant and fishing vessels lost in conflicts of the 20th Century, resulting in the deaths of 46,000 crew. The 2,535 trees each represent a ship lost during WW2.
There is also a memorial at Tower Hill to those with no known grave.
https://www.cwgc.org/visit-us/find-cemeteries-memorials/ceme...