F-7A, F-7B, and Ferret Aircraft
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The dozen aircraft delivered to the squadron for initial overseas deployment were type "F", model "7", series "A": F-7A. These were photographic conversions of B-24J's made at the Northwest Airlines Modification Center, St. Paul, Minnesota in the fall of 1943, and delivered to the squadron at Will Rogers Field, Oklahoma City, Oklahoma in January 1944. Features of the F-7A are listed below.

In the navigator/bombardier area:

  • Windows and mounts for a tri-camera arrangement of one vertical and two oblique mapping cameras (this setup was called a trimetrogon, or a trimet, as it used three cameras, each with Bausch & Lomb's Metrogon lens)
  • A modified bombardier's panel, serving as a local control point for the trimetrogon cameras
  • An intervalometer to simultaneously trigger the trimetrogon shutters at a dialed-in interval

In the forward bomb bay:

  • Auxiliary fuel tanks, port and starboard, for increased range
  • Bomb bay lights

Aft bomb bay converted to camera bay:

  • Bomb racks removed
  • Bomb bay doors fixed shut
  • Level floor installed
  • Windows and mounts for reconnaissance cameras at a vertical station (starboard) and a split vertical station (port) in the forward end of the bay
  • Aerial photographer's viewfinder and chair aft of the starboard camera station
  • Main camera control panel to the right of the photographer's seat
  • Intervalometers for the two camera bay stations
  • A work table and racks for camera magazines and film rolls in the aft corners of the bay
  • Camera vacuum circuit, bay heaters, overhead lighting, and intercomm connections

In side views, F-7A's can be identified by the oblique camera windows below the navigator compartment side windows.

Left side view of F-7A 42-64051An F-7A. This is 42-64051, "T.S.", with the blue reconnaissance camouflage paint half removed, late May or early June 1944. Note the prominent left oblique camera window and its surrounding patch in the nose area (vertically below the navigator's window and to the left of the nose art).


In May 1944, after barely seven weeks of combat operations, the squadron wrote a three-page report titled: Analysis and Recommendations regarding the F-7A type aircraft assigned to the 20th Combat Mapping Squadron, 6th Photo Group, Rcn. It included these two sentences:

"...The Tri-Metrogon set-up is inadequately protected. No provision has been made to protect the vertical camera from jarring or inadvertently stepping on it while entering the nose turret. The camera as a result, has to be realigned before each flight, also the extremely crowded conditions in the nose makes changing magazines exceedingly difficult...", and "...[The] F-7A type aircraft is inadequate in its present camera arrangement...".

These shortcomings were rectified with delivery of the first of the squadron's F-7B's in July 1944. In these, the three nose-mounted cameras of the F-7A were relocated to the aft end of the camera bay, thus consolidating all the camera equipment in one space.

In side views, F-7B's can be identified by the oblique camera windows near the rear edge of the aft bomb bay doors, one each side--and no camera windows in the nose.

Left side view of F-7b 44-42031An F-7B. This is 44-42031 over Japan after the war. (Mt. Fuji is in the background.) Note the left oblique trimetrogon window at the rear of the camera bay and the window for the split vertical station forward of it, in the belly.

(Photo: Garland Bullock, navigator in 031)

F-7B H2X

In April and May 1945, five F-7B's equipped with H2X radar were delivered to the squadron. H2X, in production as AN/APS-15, was an X-band (3 cm) radar designed to implement through-the-clouds bombing. In its F-7B embodiment, H2X was a navigation radar; that is, its radar screen displayed a picture of the ground. The retractable H2X scanning antenna was installed in place of the ball turret.

In the 20th's F-7B/H2X aircraft, a radar repeater scope was installed in the camera bay and photographed with a K-24 5" x 5" format camera. The idea was to provide bomber crews with radar screen photos which they could use in conjunction with aerial photos to identify their targets. In practice, the majority of missions flown by the squadron's H2X-equipped F-7B's were for conventional aerial photography and carried no H2X operator (Radar Observer, Bombardment).

Right rear of F-7B 44-42097An F-7B with H2X. This is 44-42097, photographed on Okinawa, 20 September 1945. It has just landed without the nose gear locked down. The retracted H2X scanner dome is visible in the position normally occupied by the ventral ball turret. (See also 44-42031 above for a retracted H2X dome.) Forward of it is the right oblique camera window for the trimetrogon (below the trailing edge of the flap).

F-7 Aircraft Data

This table lists all the squadron's F-7A's and F-7B's, their serial numbers, and the B-24 series and block they were converted from. The table accounts for all combat zone sorties (1132 total) recorded in the squadron Mission Reports and/or Final Mission Reports.

F-7 Crews

From late April 1944 until mid-February 1945, F-7A's and -B's were operated with 11-man crews. After that, 10-man crews, using four instead of five gunners, were used.

In the crew list below, the common Military Occupational Specialty code and title for each crew position is given in parentheses.

  • Pilot (1024 Pilot, Four-engine Aircraft)
  • Copilot (1024 Pilot, Four-engine Aircraft)
  • Navigator (1034 Navigator)
  • Flight Engineer (748 Army Airplane Mechanic-Gunner, Flight Engineer)
  • Radio Operator (757 Radio Operator-Mechanic-Gunner)
  • Photographer (939 Aerial Photographer-Gunner)
  • Nose Turret Gunner (611 Aerial Gunner or 612 Airplane Armorer-Gunner)
  • Ball Turret Gunner (611 Aerial Gunner or 612 Airplane Armorer-Gunner)
  • Two Waist Gunners (611 Aerial Gunner or 612 Airplane Armorer-Gunner)
  • Tail Turret Gunner (611 Aerial Gunner or 612 Airplane Armorer-Gunner)

All enlisted crewmembers were trained as aerial gunners.


In mid-June 1945 the squadron primary mission was changed from combat mapping to photographic and radar reconnaissance. As a result, the 20th Combat Mapping Squadron was redesignated as the 20th Reconnaissance Squadron, Long Range, Photo-RCM. To execute the RCM (Radar Countermeasures) mission the squadron received four B-24J ferret aircraft: Ferrets #10, #11, #12, and #13. Ferret #13 came from prior service with the 308th BG, Fourteenth Air Force, in China. Ferret #12 previously served with the 7th BG, Tenth Air Force, in India. Ferrets #10 and #11 operated in the SWPA before being assigned to the 20th.

The 20th's ferret missions were flown to detect Japanese radar installations, pinpoint locations and determine intercepted radar characterisitcs (transmitter frequency, pulse repetition frequency, and pulse width). This intelligence could then be used to find and destroy, or to jam, those same sites.

Ferret modifications to B-24's were similar to those of F-7's in that bombing equipment was removed, auxiliary fuel tanks were installed in the front bomb bay, and the rear bomb bay was converted into equipment space. Entries in the ferret flight Final Mission Reports indicate these aircraft carried sufficient gear to scan the radio spectrum from .55-6000 Mc/s (MHz). Specific equipment identified, due to failure of it, included: AN/APR-5A (Radar Search Receiver, 1000-6000 Mc/s), AN/APA-11 (Radar Pulse Analyzer), and SCR-717C (10-cm Air-to-Surface Vessel radar, used for navigation). D/F (direction finding) is mentioned in each mission report, but no specific type of equipment is mentioned.

Ferret Aircraft Data

This table lists the ferret serial numbers, the B-24 series they were converted from, the ferret numbers, and number of sorties flown.

Of the 12 ferret sorties flown before war's end, two were the squadron's longest: 15 hours 45 minutes, and 15 hours 20 minutes (to Formosa and Hong Kong). Ten of the 12 sorties were flown directly from Clark Field, Luzon. The remaining two, to islands between Okinawa and Kyushu, were staged from Yontan Strip, Okinawa, to maximize available time over target.

The 20th's Aircraft Losses

This table summarizes the 20th Combat Mapping Squadron's aircraft losses. Source is monthly Squadron History reports unless otherwise noted.

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This page was last updated August 9, 2009