We are not certain when the term "Fulda Gap" began to be used in military circles to speak of the prominent terrain corridor that runs from what used to be East Germany toward Frankfurt. Some of us remember hearing it in the 1960's. We do know that by 1980 the term was in broad use all the way up to NATO.
The core of this corridor begins in the region of Erfurt-Eisenach and crosses the Border in the Phillipstal-Rasdorf sector (the sector between our OPs xxxx and Alpha). From there it runs west to the gap between the Vogelsberg and the highlands north of the Autobahn. The broad corridor that begins at that gap and runs astride the autobahn all the way to Franfurt and the Rhine is known specifically as the Wetterau Corridor. When you reflect on the last month of World War II you will recognize that the Wetterau Corridor and what we now know as the Fulda Gap served as the main avenue for the drive of the Third U.S. Army from its Rhine bridgehead near Frankfurt onward to Leipzig and the heart of Germany. (At one point in April 1945 Third Army HQ was in Hersfeld.)
In the Cold War Soviet war planners from the Eight Guards Army Staff near Weimar all the way to the Ministry of Defense in Moscow probably had a codename for this avenue in the westbound mode. Maybe it was "Rhinegate". (We will update this line when we learn exactly what they called it.) Anyway, you do not have to be a war planner to look at the map of Germany and recognize that the shortest** route from East Germany to the Rhine River was THIS avenue. ** see map
(The alternate avenue, the North German Plain - region between the Berlin-Cologne autobahn and the North Sea coast, is traversed by two major rivers and a maze of shipping canals with steep banks. Its is about twice as long as the Fulda Gap and its reaches the Rhine where it is about twice as wide as in the Frankfurt - Wiesbaden sector.)
If the Eight Guards Army was deployed to forward positions before the outbreak of war its engineers would have needed bridging for only one secondary river, the Fulda, and that river was sometimes fordable in late summer. For the more probably scenario, a short warning attack (with no preliminary deployment from kasernes and training areas), some bridging could also have been needed for the Werra River.
When US military planners first found a need for a name to identify this probable axis of Soviet attack there may have been a debate as to whether it should be named for Fulda or Bad Hersfeld. Probably it was resolved in favor of Fulda because that was the better known city and its name was more user friendly (easier to say and write).
(If you can shed more light on when and how this name was adopted please let us hear.)