Radar Altimeters were different from today's Radio Altimeters and were used at cruising altitudes to refine a technique known as "Pressure Pattern Flying".....I think.
These radio altimeters were known as 'high range radio altimeters' and were thus used to refine pressure pattern navigation.
This is a professionals Navigator's specialty, and I have used PPN in the Pacific on Lockheed L1649 Constallations, years ago.
Works just fine....but not of course with the fixed tracks in use today, in many areas.
Longer track miles (usually), shorter time enroute.
Superb.