NavList:

You jogged another memory with that interesting analysis of early tube radios. Another joy of Pre GPS marine radio was the RDF. 

From a book called Splendid Sisters:

"The next(second) meeting of the Northern Star and the Souhern Cross was on Feb 9th, 1964, at 2 50 PM, about 430 miles north-east of St Helena in the Atlantic.

...........

When the Cross and Star met for the second time Edmeads and Baber (the masters) located each other at 7 am on their direction finders, 220 miles apart. The Cross, three days out from Cape Town, was one degree to starboard of the Star, seven days out of Las Palmas. They kept dead ahead, closing at about forty knots and picked each other on their radar screens at a distance of about twenty eight miles, reporting their respective readings by radio telephone. The ships were visible fifteen miles apart in dull, grey weather, the Start forging through thin, rainy mist."

How times have changed. If I go to the flightradar24 web site I can see photos (taken from one aircraft while mid-ocean) of another passing overhead with a few thousand feet of vertical separation.

Finally, I wonder if the expression GPS  has become a word like Biro (ball point pen) or Hoover (vacuum cleaner). I cannot recall the technical term for a proprietry word that becomes a generic term. I ask this because recently I was watching a TV program about the Lighthouse of Alexandria and the commentator casually referred to it as the GPS of the ancient world.