While the B-24 was built in larger numbers than any other multi-engine plane in the US arsenal and was factory- and field-modified into many useful configurations, its history and evolution were not nearly so well documented in the contemporary press as its sister, competitor, bomber the B-17.
The examples below are educated guesses in many cases, based on information in Jane's, Hess, et al, and Wikipedia. IDs for specific models are mostly drawn from Joe Baugher's page (http://www.joebaugher.com/usaf_serials/usafserials.html and links), based on tail numbers.
Many wartime photos had some or all of the armament, and often tail numbers or other identifiable features, dodged out; dorsal turret and tail guns were usually shown, however.
It is probably worth noting that none of the photos from my magazines shows the waist guns deployed. So the difference between the open-window, back-to-back deployment of the early models and the glassed-in, staggered deployment of the late models is not obvious indeed, is not visible in any of these photos, unlike the case with the B-17.
XB-24: The prototype was reconfigured a number of times in development.
An August, 1942, ad shows the rightside nose and inner engine nacelles. Plane is in natural metal finish, has short nose, no "football," no dorsal turret, round (non-turbocharged) engine nacelles, no "rams-horn" pitot tubes.
YB-24/LB-30A Liberator: A photo from a March, 1942, ad shows a plane from 2 o'clock high. Plane has short nose, no tail turret, no dorsal turret, round (non-turbocharged) engine nacelles, RAF markings. This plane has a "football," has "rams-horns" at 3-and-9 o'clock positions on nose immediately aft of greenhouse.
- One of the earliest photos, shown in an August, 1940, ad shows what is probably a B-24A, seen from 2 o'clock high. The plane has short nose, no tail turret, no dorsal turret, no "football," round (non-turbocharged) engine nacelles. It has "meatball" insignia and striped rudders. "Rams-horn" pitot tubes on the nose section are not evident. Sighting windows for ventral tunnel gun are not evident. The ad mentions "planes in this series, built for the US Army Air Corps," and earlier models were not produced in volume for the AAC.
- February, 1942, ad; plane seen from 10 o'clock low, has "meatball" insigne on fuselage, "rams-horns" at 3-and-9 o'clock positions, tail gun station but no tail turret.
B-24C: Short-run version leading up to the definitive B-24D.
- An August, 1942, ad from Consolidated features a drawing of what is probably a B-24C, seen from 10 o;clock high. Plane has dorsal and tail turrets, single flex gun in nose, "meatball" insignia and striped rudders, no "football"; "rams-horns" are not evident.
B-24D/PB4Y-1/Liberator B.III: The workhorse model, produced in considerable quantities, and apparently in a variety of configurations:
- The Wikipedia reference photo, from the af.mil site, shows B-24D-7-CO 123828 with no dorsal turret.
- A November, 1942, ad from Consolidated shows B-24D-10-CO planes on the production line, looking in at the left wing root.
- A December, 1942, ad shows B-24D-CO 111717 from 10 o'clock high. Plane has "meatball" insignia, "rams-horns" at 3-and-9 o'clock positions, etc.
Armament was one of the areas where visible changes happened most frequently.
- Nominal forward armament was one .50-caliber machine gun in the nose: low and central in the greenhouse, below the bomb-aiming window; central to the greenhouse above the bomb-aiming window; small side window in the left side of the nose, just aft of the greenhouse.
- Photo from a May, 1943, ad shows a B-24D from 2 o'clock high. It shows a single gun in what is apparently a flexible mount on the upper central position.
- Photo from a July, 1943, ad shows 4 B-24Ds in formation. The plane in the foreground (marked "4") seems to have a flexible mount central in the greenhouse.
- A color October, 1943,Gallery photo shows a B-24D from 2 o'clock high. Nose has single flex mount at low-central position, astrodome, "rams-horns" at 10-and-2 positions. The plane appears to have tunnel-gun windows, tail turret.
- A color October, 1943,Gallery photo shows a B-24D from 2 o'clock. Plane has a single flex mount in one of the side panes of the greenhouse. Plane has astrodome, no apparent tunnel-gun windows. Tail number is not legible.
- Before the B-24H and -J introduced the powered two-gun turret in the nose, many planes were equipped with three flexible-mount machine guns in the nose.
- A June, 1943 Gallery photo shows B-24D Eager Beaver with a three-gun nose installation. Two of the guns have protective covers. "Rams-horns" have moved to 10-and-2 o'clock positions. Nose has an astrodome.
- An April, 1944, ad features a color photo of the nose of a B-24D from below the outer left wing. The photo shows two guns of a typical three-gun setup. "Rams-horn" is at 2 o'clock position, but appears more nearly horizontal than is typical in other photos.
- Tail armament was a bit less variable, but there was the ventral tunnel gun, a single flex mount at the tail station, or the tail turret.
- A color cover photo for October, 1943 is a detail photo of the tail turret of a B-24D. Apparent sister ship B-24D-1-CF 263764 is in the mid ground. 764 and sister plane in background have tunnel-gun windows
- A November, 1943, ad shows B-24D-13-CO 123928 from 4 o'clock. Plane appears to have single flex-mount in the tail, has "star and bar with red border" insignia. The nose is distorted from the paste-up.
B-24E/Liberator IV: Essentially a B-24D built at one of the auxiliary plants Consolidated Fort Worth, Douglas Tulsa, Ford Willow Run (which supplied kits to the other plants for final assembly.) Because the B-24D was built in such large numbers, there were a number of visible configuration differences, especially considering field mods.
- June, 1942, news clip showing "first B-24 land bomber to roll from assembly line at Consolidated Aircraft's new plant 'somewhere in the southwest.'" Plane is seen on flightline from 11 0'clock, has long nose with no astrodome, dorsal turret forward of wing spar, oval (turbocharged) engine nacelles. Insignia are not visible and tail number is illegible.
This should be a B-24E-10-CF.
- July, 1942, ad showing "Ford-built bomber O-1" on the flightline, seen from 11 0'clock. Plane has "football", dorsal turret, "rams-horns" at 3-and-9 o'clock positions on nose, oval nacelles; appears to have "meatball" insigne on fuselage; bomb bay doors are open; tail is not visible.
This should be a B-24E-1-FO.
An October, 1943, news clip is a detail photo of the Emerson nose turret on a Willow Run plane.
A December, 1943, ad shows a B-24H (probably B-24H-1-CF 264438 the tail number is difficult to read) from 2 o'clock, with a clear picture of the Emerson nose turret.
The plane appears to retain the tunnel-gun windows (lower aft fuselage).
Photo from a December, 1943, ad is a detail photo of the Emerson nose turret.
A January, 1944, ad shows B-24H-1-CF 264435 from 2 o'clock high and a detail photo of the Emerson nose turret. Plane has astrodome, "rams-horns" at 10-and-2 positions. It appears to have tunnel-gun windows.
A February, 1944, ad shows B-24H-1-FO 27614 from 10 o'clock, Plane has Emerson nose turret, "rams-horns" at 10-and-2 positions, star and bar with red border insigne on fuselage.
A May, 1944, ad shows a B-24J from 10 o'clock high. Photo shows dorsal, belly and nose turrets; nose turret appears to be Consolidated A-6 type.
An August, 1944, ad shows a PB4Y-1 from 10 o'clock high. Plane has midships astrodome, ERCO bow turret.
A November, 1944, ad shows a PB4Y-1 from 11 o'clock low. Plane has ERCO bow turret and appears to have ASV radar installation.
- A color cover painting for April, 1945 shows a PB4Y-2 in flight from 2 o'clock high.
- A color photo from a June, 1845, ad shows a PB-4Y-2 from 10 o'clock high.
C-87 Liberator Express: Cargo plane derived from the basic B-24 design, produced on the same production line (Fort Worth) as B-24D (and later models). C-87s were used for cargo, troop transport and VIP transport.
- An October, 1942, news clip shows a C-87, described as rolling off the production line more than a month ahead of schedule, on the flightline, seen from 2 o'clock.
Plane should be a C-87-CF.
- A January, 1943, ad from Consolidated shows C-87_CF 111639 from 10 o'clock low. Plane has "rams-horns" at 3-and-9 o'clock positions.
- A photo from a May, 1944, ad shows the aft left fuselage of C-87-CF 330566 with cargo doors open. Photo shows hold-open and insulation on doors.
RY-3 Liberator Express:
- All models except the XB-24K, B-24N, PBY-4-2, and RY-3 had the twin-tail empennage.
- Models through B-24E had "greenhouse" nose. Later versions had a small window on the left side just aft of the greenhouse, which served as the point for one of the three guns in the three-gun nose.
- B-24G (built by North American at Dallas), B-24H (built by Consolidated at Fort Worth and by Ford at Willow Run), B-24J (Built by Consolidated at San Diego and Fort Worth, by North American, by Ford, and by Douglas at Tulsa), and B-24L, -M, -N, plus all PB4Ys, all had power nose turrets with two .50-caliber machine guns. Some B-24Ds were field modified to mount a tail turret in the nose.
- Field-modified planes and San Diego-built planes mostly had Consolidated A-6 turrets; these were hydraulically driven. Recognition feature is the angled flat-plate aiming windows
- Most Ford-built planes, plus Douglas-built, North American-built and most Fort Worth planes had
Emerson A-15 electrically-driven turrets. Recognition feature is vertical aiming windows.
- PB4Y versions had ERCO bow turrets. Recognition feature is that they look almost spherical.
- B-24B through -D went through a variety of configurations for protection from attack from the rear.
- Some planes had single or dual flexible-mount at the tail-gun station, Early .30-caliber guns were upgraded to .50-calibers.
- During the transition from flexible mounts some planes had .50-caliber guns in a ventral tunnel. These planes can be identified by small windows under the aft fuselage, just forward of the empennage.
some of the fuselages built to accommodate tunnel guns were converted to tail turrets, but the windows were still present.
- Later models all had Consolidated A-6 turrets, until B-24L, which had the Tucson-developed two-gun, manually operated turret and the B-24M and -N, which had a Motor Products turret.
- I picked up the "rams-horn" pitot tube nickname from an Internet forum. They moved around a bit over time.
- They don't seem to be visible in photos of the prototype.
- Early, short-nose, planes tended to have them mounted about midway up the sides of the nose (9-and-3 positions).
- Later, they moved up to the "shoulder" of the nearly rectangular fuselage (10-and-2 positions); some mounts were nearly horizontal, some close to 45° from the horizontal.
- Some late photos seem to show them mounted further around the curve of the shoulder and more steeply slanted.