Dan Foster wrote

Just out of sheer curiosity, what made 100' AGL suitable, but
not higher altitudes? Climb performance, density altitude,
weight limits?

A lot of the time, it was the limited range of the Magnetic
Detection equipment for tracking a submerged submarine. The
lower you flew. the better your chances of maintaining contact.
Hell....the S-2Fs were flying lower than we were, but they
only had a 4-6 hour mission. :-) Airline flying was a Piece of
Cake compared to anti-submarine work. I thought that I had
died and gone to heaven when I joined PanAm. :-)

Bob Moore