"a nightingale come over on the Cunard or White Star Line"

In the days before widespread commercial aviation, international travel was undertaken on vast ocean liners. The Cunard and White Star Lines were rival shipping companies.

Cunard, an Anglo-American company, was founded in 1840. Among its famous ships were the RMS Lusitania, launched in 1907 and sunk by a German torpedo missile in 1915, and the Mauretania, launched in 1906.

The White Star Line was a British shipping company founded in 1869. Its most famous ship was the ill-fated RMS Titanic, which sank in the North Atlantic in April 1912. 

White Star merged with Cunard in 1934.