The Navy used the B-24 in two versions the PB4Y-1 which was a
regular twin tailed B-24 and the -2 version. ABout 850 -2 models
were made mostly at the end of WW-II. The single tail version of
the B-24 was slightly more efficent than the twin tail version
but not enough to go thru the trouble of changing the production
lines in the middle of the war. Almost forgot, the reason for
the two top turrets was the Privateers were used in a lot of low
level attacks on shipping. If enemy fighters appeared the PB4Y
would drop down to the surface of the ocean or land. This tactic
put the attacking fighters at a disadvantage and would of course
negate the need for ventral protection. Ah what the heck, I went
and found a PB4Y-2 pic from 1949 showing the top two turrets and
this one has Emerson nose and tail turrets, I think. A small
number of PB4Ys are still in service, I think, as Fire Bombers.
Hawkins & Powers in Wyoming operated about half a dozen
Privateers as recently as 2002. two turret guns on top. Wonder
why? Proba