F-89 turret

From May 1981 issue of "Airpower" magazine:

1 & 2. F-89A (N2007) AF49-2434 modified for the installation of the Martin
turret. A sizable installation even for an airplane the size of the
F-89, the turret extends forward from the aft edge of the black band painted
on the nose, in effect, a total structural/weapon system replacement for the
6-gun nose normally installed on the F-89A/B/C aircraft. The Martin turret
was GFE (Government Furnished Equipment), an armament and fire control
system independently developed in parallel with the Curtiss XP-87 and
Northrop XP-89 and specified for ultimate installation in these aircraft
according to the Army Air Force "Military Aircraft Characteristics," dated
23 November 1945. The Glenn L. Martin Company of Baltimore won the design
and development contract under the contract designator MX-852. This fire
control system was designed for application in F-89 class aircraft and for
bomber defense. The F-89A shown is the only known application to a fighter,
but the system was reportedly test flown in a B-17.