LONDON — Britain on Saturday honored members of the so-called Windrush generation, people from the Caribbean who were encouraged to migrate here to help the country rebuild after World War II, but struggled to prove their citizenship in a recent immigration crackdown.

On Saturday, which was declared the first National Windrush Day, Prime Minister Theresa May of Britain announced that a memorial to their efforts would be built at Waterloo Station, where many immigrants first arrived in London after docking at Southampton. It was also where they met friends and family member who had already settled in Britain.

Mrs. May called the occasion an “annual opportunity to remember the hard work and sacrifice of the Windrush generation.”

“They crossed an ocean to build a future for themselves, for their communities, and above all for the United Kingdom — the country that will always be their home,” Mrs. May added.