Bjørnar Bolsøy wrote:

I'm a bit unclear on one thing, was the 0.50 quartet replaced
by the m61 on all the B52s and then, subsequently, removed from
service in the early 90s?


The gatling gun only appeared on the H model- other B-52 models
continued to carry the 4 x .50 installation until their retirement
(unless some G's stayed around long enough to have them removed),
IIRC.

The gun installation was finally removed due to the changed
threat, which presumably would no longer be from enemy aircraft
closing to within the range and field of fire of the removed
gun.

Mike