'Mule' deck tractors in 1/72 scale
Designations
My limited understanding of the vehicle's designations is that the original yellow-painted Mules were designated MD-3, MD-3A and MD-3B, and that the improved (Service Life Extension Program, SLEP) white-painted Mules are designated A/S32A-31, A/S32A-31A and A/S32A-31B (see Aeronautical and Support Equipment Type Designation System for an explanation of these codes). The SLEPed version can be identified easily by the widened rear of the vehicle (some 6 inches) and a sloped rear edge (like a car 'spoiler'). The Verlinden, Fujimi and Maquettes Dauzie Mules are the original version, only DreamModel offers the later wider version.
Note that there was a short period where the 'old' version was painted white, because the Navy phased out the yellow paint that contained lead (or maybe cadmium?). Judging from the occurence of both versions in Verlinden's 'Lock-on No 14: USS Forrestal' from 1991 (possibly the contents were photographed in 1990), the switch occured around that time.
All kits I've seen have single rear wheels. But I'm sure the real thing has double wheels. Possibly the 6 inch widening also has to do with the rear wheels, creating a wider track, or the use of wider tires.
Confusingly, the US Air Force also has an MD-3: "The MD-3 Generator Set is a portable unit designed to furnish AC and DC electrical power for the starting of aircraft, and for ground maintenance". It's definitely not a tractor, so the two can't be confused.
History
The Mules used to be known as MD-3s, but are now officially known as the A/S32A-31. I found a few Navy manuals with some information.
Quoting from 'Aviation Support Equipment Technician (ASE 3&2 AND ASM 3&2), Volume 1, Basics' (NAVEDTRA 103245), 1981 edition, page 6-5:
"MD-3 TOW TRACTOR - This tractor was designed for use aboard aircraft carriers and will handle any type of carrier-based aircraft. It can configured as an MD-3 (basic tractor - no gas turbine power unit), MD-3A (mounts a GTCP-100-54 gas turbine power unit), or MD-3B (mounts a GTC-85-72/73 power unit)."
Quoting from 'Aviation Support Equipment Technician (ASE 3&2 AND ASM 3&2), Volume 1, Basics' (NAVEDTRA 103245), 1981 edition, page 6-25:
"SB/TAU-2 FIREFIGHTING UNIT - The TAU-2 is a self-contained twin agent firefighting unit designed for shipboard use. The assembly is mounted on the rear of an MD-3 tow tractor for flight deck use or it is mounted on an Aero 21C bomb skid for hangar deck use. The TAU-2 consists of two tanks, an 80-gallon tank for premixed Aqueous Film Forming Foam (AFFF) Solution (commonly referred to as light water) and a 200-pound capacity tank for Potassium K Power (PKP) chemicals. The solutions, PKP and light water, are both propelled from the tanks through associated piping by a single 400-cubic foot capacity nitrogen cylinder. The nitrogen cylinder must have a charge of 1700 to 2400 psi at 70 degrees Fahrenheit for proper operation of the unit. The solutions are dispensed through a 100-foot non collapsible twin hose and twin pistol grip nozzles. The hoses are bound together and enclosed by a cotton cover." (TAU is short for 'twinned agent unit')
Quoting from NAVAIR (Naval Air Systems Command) 19-40-44:
"The MD-3 Tow Tractor is a pneumatic tired, diesel powered tractor intended for towing all carrier based aircraft aboard aircraft carriers. The MD-3 tractor is powered by a 100 horsepower diesel engine and has a draw bar capacity of 8500 pounds at an approximate speed of 1 mph on a dry level concrete surface. The MD-3 includes a quick detachable unit with the capability of starting conventional and impingement type air-starting aircraft and providing AC and DC electrical power to aircraft while to towing. Hydraulic power steering is provided to permit maneuvering in confined areas. The tractors have a low silhouette to permit operation under wings of parked aircraft."
"The tractors originally came into service in the early 1950's and were manufactured by Frank Hough Corp. Around 1952, the Frank G. Hough Company was bought out by International Harvester which was later bought out by Tenneco Incorporated and merged with its then subsidiary, Case Corporation. The tractors originally procured in the 50's were SLEPed (Service Life Extension Program) in 1981 and reidentified as the A/S32A-31. This SLEP was essentially a re-engining of the unit (new engine and transmission), along with some brake components and a general overhaul (stripped all the way down and repainted)."
NAVAIR (Naval Air Systems Command) document 19-40-44 lists the following dimensions, without stating whether it's for the original design or the SLEPed version:
These measurements translate into 57.2 x 22.9 x 12.7 mm.
Verlinden
The Verlinden 1/72 resin scale model of the MD-3 'Mule' US Navy deck tractor is shown in my oldest Verlinden catalog, 'Catalog No.4' that's probably from around 1987. The box has catalog number 240 printed on the photo label, but 'Catalog No 4' also lists a secondary number, ACDA 72003. Later, probably after the move to the USA, the kit was listed as catalog number 2560. It was produced until at least 1994, since it was still listed in Verlinden catalog #13 from 1994-1995.
The model's dimensions deviate quite a lot from the numbers listed earlier: On my built example, I measured 51.7 (without hitches) x 24.8 x 14.0 (front) / 14.9 mm (rear) mm instead of 57.2 x 22.9 x 12.7 mm.
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| Shown here are all resin parts. At the front there's the 'short' tractor in one piece. The second row shows three rear side attachments, plus five detail parts (two hitches, parking brake handle, steering wheel, hitch extension). The third row shows the front and rear wheels. Also included in the kit are dry transfers, that probably stopped working years ago. Not included is the flexible hose for the APU.
I found a couple of error in the kit. The 'short' rear side attachment is too thin, and it's lower extension does not exist in reality. The cockpit opening is too wide, it should be around two millimeters narrower. The single rear wheels should be double rear wheels.
Casting quality is near perfect, with only three air bubbles on the 'long' rear extension, in positions where a raised fastener should be present. I restored them with a piece of stretched black sprue. On the casting block with small details, the steering wheel had a gap.
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| The Verlinden 1/72 MD-3 'Mule' is also available as the 'US Navy carrier fire tractor', catalog number 267 (ACDA 72004, later 2591). It has the SB/TAU-2 firefighting unit as briefly described above, as the single option to build the kit. All other parts are identical to the earlier kit.
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| The SB/TAU-2 firefighting unit is not correct unfortunately. The model basically has of a large cilindrical tank taking up the full width, a small cilindrical tank with a hollow end cap, and a rearward-facing bench for two firefighters (or hose storage). The large cilindrical tank has one spherical end cap (left), and one flatter, semi-spherical end cap (right), and that's an indicator of what's wrong. In reality there's a spherical tank on the left side, and a shorter large cilindrical tank on the right side. The spherical tank is placed slightly more aft than the cilindrical tank. Verlinden morphed them into one.
The kit comes with very flexible thin rubber cord, to make the fire fighting hoses. But no suggestion how to model the hoses is included in the small instruction sheet. Worse is that nozzles are not supplied either.
On my kit, an upper corner of the bench was broken off, but the sliver was still in the ziplock bag, so I was able to restore it. Two other small parts were broken off too, but no trace of them.
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I found a short kit review in Fine Scale Modeler, December 1987 issue. It is very favourable, but has no comments on accuracy. It reports that a photo of the depicted Mule can be found in 'Super Carriers - US Naval Air Power Today' by Montbazet from 1985. I found a photo in the later 'Supercarriers - Naval air power in action' on page 26-27.
Verlinden Modeling Magazine Volume 3, No 2 and No 3 contain articles on the real Mules.
Starting 2021 I gathered some 100 snapshots from various YouTube videos, shown below. The photos show both the 'short' version, and the 'long' version. The 'long' version had three types of APUs attached. Unfortunately I do not know which is which (see gas turbine versions listed above), so I called them Type 1, 2 and 3. The Verlinden APU attachment looks a lot like Type 2. For the 'short' version, a ballast plate is missing, but funnily if you would cut off the 'bumper' and rotate it 90 degrees, you're 90% done. Also, a simpler tow coupling is missing: a simple C-bracket with a pin through it.
Fujimi
The Fujimi 'Deck crew set' (catalog number 35001) turned out to be quite a surprise. With regards to details, this injection moulded MD-3 was a near 100% copy of the Verlinden model! Of course Fujimi had to break up Verlinden's single-piece main casting into several smaller parts, but otherwise the differences were very, very small. The hood has a fold on the centerline (that I have seen in only one photo of the real thing, the rest had slightly bulged hoods), but otherwise it is identical, down to the tiniest details. The Fujimi model also has the incorrect 'rear bumper' for the short version like Verlinden, and the fire-fighting attachment has the same incorrect large tank, which further reinforces the impression that the kit is a copy.
Alternatively, both Verlinden and Fujimi could have used the same set of drawings to create their models. I've been told that Modell Fan once had Mule drawings. On the other hand, I was quite amazed that it was possible for Fujimi to achieve the same detail level with injection moulding. Another lesson learned!
The Fujimi Mule can be built in three versions, the short version, the version with a 'Huffer' extension similar to Verlinden, and the fire-fighting SB/TAU-2 attachment as described above. The first and second are also found in Verlinden #240, the last is similar to Verlinden #267. On the latter, Fujimi copied the wrong tank layout of the Verlinden model.
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| The oldest proof of existence that I found of the Fujimi set is a 1990 catalog, but I don't have catalogs of 1987, 1988 and 1989 (it's not shown in the 1986 catalog). The MD-3 is also listed in my 1994, 1995, 1996, 1997 and 2001 Fujimi catalogs. In 2008 or 2009, the Mule tractor was included in a reissue of on Fujimi's VF-96 F-4J.
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Testors
The Fujimi set was also issued by Testors in the USA, with catalog number 850, with photo box-art. Possibly it was also sold bagged, with a black and white header card based on the Fujimi box art.
Maquettes Dauzie
In 2007 I bought a Maquettes Dauzie resin 1/72 scale US Navy tow tractor (catalog number 72 006) at the IPMS-NL Nationals. The oldest reference I found so far is an August 1986 advertisement in Scale Aircraft Modeling. Compared to the Verlinden/Fujimi MD-3, it has a different unit attached to the rear side. Also included are parts to make the air starter's hose, in the shape of a piece of hose, and metal wire to wrap around it. Judging from the exhaust location on the right side, the APU is like Type 1 in the reference photo section below. However the details on the left side are of Type 2 if I am not mistaken. The same tractor was also available without the APU unit at the rear (catalog number 72 007).
The length and width of the complete vehicle are around 15% less than the Verlinden/Fujimi Mule, which makes you wonder who used the correct (or best) data. I obtained some more MD models, and the dimensional errors in them are so obvious that my trust in MD's master builder has disappeared largely. Therefore I believe the Verlinden/Fujimi Mules are more accurate.
DreamModel
In 2008, DreamModel from China issued four resin Mule kits, with photo-etch details and decals. The versions are old & new short style, and old & new long style tractors. The new style tractors have increased rear track, and slightly widened fenders to match.
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| 0201 (old & long)
| 0202 (new & long)
| 0203 (new & short)
| 0204 (old & short)
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PhantomModels
In 2013 PhantomModels from Moscow issued a resin Mule kit, with photo-etch details and decals (catalog number 7002). It represents the updated version with increased rear track, and slightly widened fenders to match.
Hobby Master die-cast
Hobby Master released a diecast Mule in a blister packaging. It comes in two versions: the 'US Navy Tow Tractor' (catalog number HD2002) featuring an MD-3A with two figures, and the 'US Navy Fire Tractor' (catalog number HD2003) featuring an MD-3 with the fire fighting attachment, in white and red, with two figures. It appears that the same sets were sold in cardboard boxes with a 'B' extension to the catalog number. The two versions are also sold together as 'Modern aircraft carrier diorama' (catalog number HD1002).
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| HD2002
| HD2003
| HD2002B & HD2003B
| HD1002
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Kit comparison
I only have the Verlinden and Fujimi kits, and built the Verlinden kit. Of these two the Fujimi kit seems to hold the edge - some advantages:
the Fujimi kit allows the construction of all versions of the Verlinden kits
the Fujimi tires are nicer
a towbar and wheel chocks are included
an air hose is included, whereas Verlinden only gives instructions how to make the hose from scratch
Colors
Somewhere during the early nineties, the color of US Navy deck vehicles switched from yellow to white. Alex Suvorov's excellent webpage U.S. Navy Flight Deck Tractor Models claims the colors were FS 33538 Orange Yellow and FS 17875 Insignia White. Humbrol 197 and Revell 310 (both RAL 1028 matches) come quite close to the former.
MD-3 'short' tow tractor
This Mule looks brand new to me. In the source movie, the Enterprise looks like it's on shakedown, with only a few aircraft on board. This makes it from the early sixties.
Snapshot from video Inside The Big E
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MD-3 with type 1 APU
| Probably filmed on board the Kitty Hawk (CV-63). The Oshkosh MB-5 fire truck is also of note.
Snapshot from video Task Force 77 (1970)
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Mule driver relaxing, with the rearr of two other Mules visible. Probably filmed on board the Kitty Hawk (CV-63).
Snapshot from video Task Force 77 (1970)
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| Mule with Type 1 APU towing an A-7. Probably filmed on board the Kitty Hawk (CV-63).
Snapshot from video Task Force 77 (1970)
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Nice detail view of a well-maintained Mule onboard CVN-68 Nimitz. The air hose looks a bit worn though.
Snapshot from 'The Final Countdown' from 1980
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| The same Mule, now seen from the rear. Contrary to nearly all photos previously shown, this Mule appears to have an additional air inlet on the top side. Or maybe it's a missing panel? Note the double red turbine warning stripes on either side. But how can the turbine wheel(s) be so close to the inlet side? Or do the stripes signify an area where you could be sucked against the inlet openings?
Snapshot from 'The Final Countdown' from 1980
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Another Mule onboard CVN-68 Nimitz, with what looks like an improvised sheet aluminum door (with material codes printing it seems) lacking the louvres. The small door ahead either fits badly or is partly open.
Snapshot from 'The Final Countdown' from 1980
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| A very clean Mule on board of USS Enterprise CVN-65.
Snapshot from 'The Hunt for Red October' from 1990
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MD-3 with type 2 APU (like the Verlinden model)
A shot from the early sixties. Note relatively few markings during the initial use. The Mule at the left has its wheels painted in a different color.
Snapshot from video Inside The Big E
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| This is probably the same Mule as in the above shot.
Snapshot from video Inside The Big E
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Interesting rear view, with some kind of attachment on the rear's top. The Mule at the rear is shown in the Type 3 APU section.
Snapshot from video Operation Saratoga (1965)
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This one has no rounded extension on top of the extended bumper, like many above. Instead there are some small-section beams against the rear side, plus some kind of basket.
Snapshot from video Hot Shots! - Highway to the Danger Zone
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MD-3 with type 3 APU
Both Mules have the APU in a 'raised' position, well above the deck of the tractor itself. The combination of the gusset in the tractor's extension and the triangular rear leg of the APU creates the trapezoid shape, that is the easiest identification feature of this version.
Snapshot from video Discovery Channel Wings - A-4 Skyhawk
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| This looks like the same APU unit to me, but now lowered and flush with the tractor. The trapezoid is accordingly lower. However it looks like the APU is wider than the tractor.
Snapshot from video Ready On Arrival (1966)
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The left side also shows the trapezoid opening. Again the APU appears to be slightly wider than the tractor.
Snapshot from video Ready On Arrival (1966)
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MD-3 with type 4 APU ?
There may be yet another type of APU attachment, or maybe it was a fire-fighting unit, considering it was painted red, plus what look like rolled-up fire-fighting hoses. So far only one picture has surfaced, on the USS Coral Sea tribute site (find courtesy of Jari).
MD-3 with SB/TAU-2 fire fighting unit
Two comments on the fire fighting version:
1. I think that all kits got the tank configuration wrong. The real vehicle has a sperical tank at the left, and a cilindrical tank with semi-spherical ends at the right and center. The models combine these two. There's also a small nitrogen tank at the very rear.
2. The original version had a simple bench at the rear, for two additional fire fighting crew. As far as I can tell, this was often converted to a storage for the firefighting hoses, by adding a few square-tube elements (as indicated in the Verlinden model). I rare cases, a new seat (or seats) were added behind the framework, to restore the seating capacity.
Great overall view of a white firefighting Mule onboard CVN-68 Nimitz. It looks like there's a high-pressure steel vessel with a concave bottom, behind the large tank.
Snapshot from 'The Final Countdown' from 1980
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| The same Mule, now seen in a perfect side view. The fire fighting hoses can be seen clearly; they appear to be folded double.
Snapshot from 'The Final Countdown' from 1980
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Partial rear view, showing the Spartan rear seating area. There's a pintle mounted on the rear bumper, probably for secondary towing duties.
Snapshot from 'The Final Countdown' from 1980
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| The Mule after coming to a stop. The serial probably reads 904748. There's a small strap holding the fire fighting hoses down.
Snapshot from 'The Final Countdown' from 1980
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Great detail view of the rear of a fire-fighting Mule. The pintle and rear lights are clearly visible.
Snapshot from 'The Final Countdown' from 1980
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A rare photo of a fire-fighting Mule in the role of tow tug, probably filmed on board the Kitty Hawk (CV-63). The spherical tank can be seen here.
Snapshot from video Task Force 77 (1970)
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| A rather vague shot from the island, also probably filmed on board the Kitty Hawk (CV-63). It is standing by next to an Oshkosh MB-5 fire truck. If you look closely, the two tanks can be distinguished. They are slightly offset from each other.
Snapshot from video Task Force 77 (1970)
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A rather bare yellow Mule with the SB/TAU-2 firefighting unit from the 1972-1973 timeframe, standing guard during launch operations.
Snapshot from video USS Midway Flight Operations 1972 73
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| An interesting all-red Mule with the SB/TAU-2 firefighting unit, the tank of which appears to have a slightly different tone of red. On the back something resembling a hose reel can be seen.
Snapshot from video USS Midway Flight Operations 1972 73
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| A yellow Mule with the SB/TAU-2 add-on in red. However the large tank is purple, a variation not seen before.
Snapshot from video VA-164 USS Hancock 1972
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From the same film, an all-red fire-fighting Mule with again a purple cilindrical tank.
Snapshot from video VA-164 USS Hancock 1972
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| From the same film, an all-red fire-fighting Mule with a purple spherical tank.
Snapshot from video VA-164 USS Hancock 1972
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The same 'Z' or '2', now with the hood open. It appears to lack the rearward-facing bench.
Snapshot from video VA-164 USS Hancock 1972
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| One more all-red Mule with a purple tank. It's difficult to see, but there's a second crewman in full gear sitting on the rear, suggesting there is a seat or a bench.
Snapshot from video VA-164 USS Hancock 1972
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| A low-quality screenshot, but an interesting variation: an all-red fire-fighting Mule with a yellow hood, probably a replacement part. The rear seating area appears blue-purplish.
Snapshot from video USS Ticonderoga CVA14 1967-1968
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Excellent rear view of two firefighting Mules. I think we now clearly see the rear seating area. The frame on the left is a holder for a rolled-up fire hose. Its nozzle and handles are also clearly visible.
Snapshot from video A Day In The Western Pacific Aboard USS Oriskany CV-34
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MD-3 various details
| Top side view from the cockpit of an A-3 being started. APU version is unknown. It appears no anti-skid coating is applied.
Snapshot from video USS Midway Flight Operations 1972 73
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Unique view of the starter hose being pressurized, while starting an A-3. The extended tow hook on the Mule is also of interest.
Snapshot from video USS Midway Flight Operations 1972 73
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