+++ DISCLAIMER +++
Nothing you see here is real, even though the conversion or the presented background story might be based historical facts. BEWARE!
In October 1951, a heavy tank project was underway to mount an oscillating turret with an automatically loading 120mm Gun on the hull of the 120mm Gun Tank T43. (The T43 would later be serialized as the 120mm Gun Tank M103, America’s last heavy tank.). This was the T57, and the Rheem Manufacturing Company were granted a contract to design and build two pilot turrets and autoloading systems.
During the T57’s development, it became clear that it was feasible to mount a lighter armored version of the T57 turret on the hull of the 90mm Gun Tank T48 (The T48 later became the 90mm Gun Tank M48 Patton). This combination granted the possibility of creating a ‘heavy gun tank’ that was considerably lighter (and therefore more agile and tactically flexible) than any previously designed.
In May 1953, a development project was started to create such a tank. It would be designated the 120mm Gun Tank T77, and another contract was signed with Rheem to create two pilot tanks. The T77 weighed about 50 tons, with armor of the hull being up to 110mm thick. It was originally powered by a 650 hp Continental AVSI-1790-6 V12, air-cooled twin-turbo gasoline engine. This would propel the tank to a speed of 30 mph (48 km/h). The tank was supported on a torsion bar suspension, attached to six road wheels. The drive sprocket was at the rear, while the idler was at the front. The idler wheel was of the compensating type, meaning it was attached to the closest roadwheel by an actuating arm. When the roadwheel reacted to terrain, the idler was pushed out or pulled in, keeping constant track tension. The return of the track was supported by five rollers.
The T77 had a crew of four: The driver’s position was standard for M48 hulls, located centrally in the bow at the front of the hull. Arrangements inside the turret were standard, too: The loader was positioned to the left of the gun, the gunner was on the right with the commander behind him.
The T77’s oscillating turret could be easily mounted to the unmodified 2.1 m (85 inch) turret ring of the M48 hull, and on other tanks, too. It consisted of two actuating parts: a collar that was attached to the turret ring, allowing 360° horizontal traverse, and a pivoting upper part with a long cylindrical ‘nose’ and a low profile flat bustle that held the gun, which could elevate to a maximum of 15 degrees, and depress 8 degrees. It also held the complex loading mechanism and the turret crew.
Both turret halves utilized cast homogeneous steel armor. The sides of the collar were made to be round and bulbous in shape to protect the trunnions that the upper half pivoted on. Armor around the face was 127mm (5 inches) thick, angled at 60 degrees, what meant an effective 10 in (254 mm) equivalent of RHA at the turret front. Maximum armor strength was 137mm (5.3 inches) on the convex sides of the turret, and this dropped to 51 mm (2 inches) on the bustle.
Though it looked like two, there were actually three hatches in the turret’s roof: There was a small hatch on the left for the loader, and the slightly raised cupola for the commander on the right, which featured six periscopes. These two standard hatches were part of a third large, powered hatch, which took up most of the middle of the roof, granting a larger escape route for the crew but also allowed internal turret equipment to be removed easily. It was also a convenient way to replenish the ammunition storage, even though a use under battle conditions was prohibitive. In front of the loader’s hatch was a periscope, housings for a stereoscopic rangefinder were mounted on the sides of the swiveling turret part, and there was another periscope above the gunner’s position, too. Behind the large hatch was the ejection port for spent cartridges, to its right was the armored housing for the ventilator.
The initial Rheem Company turret concept had the gun rigidly mounted to the turret without a recoil system, and the long gun barrel protruded from a narrow nose. The gun featured a quick change barrel but was otherwise basically identical to the 120mm Gun T123E1, the gun being trialed on the T43/M103. However, for the T57/77 turret and the autoloader, it was modified to accept single piece ammunition, unlike the T43/M103, which used separately loading ammo due to the round’s high weight. This new gun was attached to the turret via a conical adapter that surrounded the breech end of the gun. One end screwed directly into the breech, while the front half extended through the ‘nose’ and was secured in place by a large nut. The force created by the firing of the gun and the projectile traveling down the rifled barrel was resisted by rooting the adapter both the breech block and turret ring. As there was no inertia from recoil to automatically open the horizontally sliding breech block, a hydraulic cylinder was introduced. Upon firing the main gun, this hydraulic cylinder was triggered via an electric switch. This new variant of the T123 cannon was designated the 120mm Gun T179. It was fitted with a bore evacuator (fume extractor) and a simple, T-shaped muzzle brake.
A single .30 Caliber (7.62mm) machine gun was mounted coaxially, and another such weapon or a medium 0.5” machine gun could be attached to a mount on the commander’s cupola.
Using standard Armor-Piercing Ballistic Cap Tracer Rounds, the T179 was capable of penetrating 221-millimetre (8.7 in) of 30-degree sloped rolled-homogenous armor at 1,000 yards and 196-millimetre (7.7 in) at 2,000 yards. It could also penetrate 124-millimetre (4.9 in) 60-degree sloped rolled-homogenous armor at 1,000 yards and 114-millimetre (4.5 in) at 2,000 yards.
The T179’s automatic loader was located below the gun and it gave the weapon a projected rate of fire of 30 rounds per minute, even though this was only of theoretical nature because its cylinder magazine only held 8 rounds. After these had been expended, it had to be manually re-loaded by the crew from the inside, and the cannon could not be operated at that time. Ammunition types such as High-Explosive (HE), High-Explosive Anti-Tank (HEAT), Armor Piercing (AP), or Armor-Piercing Ballistic-Capped (APBC) could be fired and be selected from the magazine via a control panel by either the gunner or the tank commander, so that it was possible to quickly adapt to a changing tactical situation – as long as the right rounds had been loaded into the magazine beforehand.
The cannon itself was fed by a ramming arm that actuated between positions relative to the breech and magazine, operating in five major steps:
1) The hydraulically operated ramming arm withdrew a round and aligned it with the breach.
2) The rammer then pushed the round into the breach, triggering it to close.
3) Gun was fired.
4) Effect of gun firing trips the electric switch that opens the breech.
5) Rammer picks up a fresh round, at the same time ejecting the spent cartridge through a trap door in the roof of the turret bustle.
Beyond the 8 rounds ready-for fire in the magazine, the main gun had only a very limited ammunition supply due to the large size of the 1-piece rounds: only 21 more 120 mm rounds could be stored in the hull and at the base of the turret.
After thorough trials, the T77 was, powered by a more fuel-efficient Continental AVDS-1790-2 V12, air-cooled twin-turbo diesel engine with 750 bhp (560 kW), accepted as a replacement for the U.S. Army‘s unloved heavy M103 and introduced as the M77. The first M77s were assembled at the Detroit Arsenal Tank Plant in March 1964. However, the M77 was primarily a support vehicle for standard tank units and reserved for special operations. Therefore, the type’s production numbers remained low: only 173 tanks were eventually built until 1968 and exclusively allocated to U.S. Army units in Western Germany, with a focus on West Berlin and Southern Germany (e.g. in the Fulda Gap), where they were to repel assaults from Eastern Germany and defend vital installations or critical bottlenecks.
Due to its high rate of fire and long range, the M77 was ideally suited for defensive tasks and hit-and-run tactics. But this was, unfortunately, the type’s only selling point: The oscillating turret turned out to be complex, concerning both handling as well as maintenance, and in practice it did not offer the same weapon stability as the M48’s or the later M60’s conventional design, especially when firing during movement. The cramped interior and the many mechanical parts of the bulky autoloader inside of the turret did not make the tank popular among its crews, either. Several accidents occurred during manoeuvers while the loader tried to refill the magazine under combat pressure. A further weakness was the type’s low ammunition stock and the fact that, despite the autoloader, there was still a loader necessary to feed the magazine. The low ammunition stock also heavily limited the tactical value of the tank: typically, the M77 had to leave its position after expending all of its ammunition and move to a second line position, where the huge one-piece rounds could be replenished under safer conditions. But this bound other resources, e. g. support vehicles, and typically the former position had to be given up or supplanted by another vehicle. Operating the M77 effectively turned out to be a logistic nightmare.
During its career, the M77 saw only one major upgrade in the mid-Seventies: The M77A1 was outfitted with a new multi-chamber muzzle brake, muzzle reference and crosswind sensors (the latter was mounted in a small mast on the rear of the turret) and an improved turret stabilization system along with an upgraded turret electrical system. All of these measures were intended to improve the tank’s 1st shot kill probability, esp. at long range. A large AN/VSS-1(V)1 white/IR searchlight was added above the gun barrel, too. All tanks in service were upgraded in this fashion, no new tanks were built. Unlike the M48, neither the M77 nor the Rheem turret or its autoloader system were cleared for export, even though Israel showed interest.
In the early Eighties, there were further plans for another upgrade of the M77 fleet to a potential A2 status. This would have introduced a laser rangefinder (instead of the purely optical device) and a solid state M21 ballistic computer with a digital databus. The M21 would have allowed a pre-programmed selection and fire sequence of different ammunition types from the magazine’s chambers, plus better range and super-elevation correction. However, this did not happen because the M77 had become obsolete through the simple depletion of its exotic 120 mm ammunition from the army’s stocks. Therefore, another plan examined the possibilities of replacing the T179 gun with the 105 mm M68 rifled anti-tank gun, a license-built version of the British L7 gun, which had, despite the smaller caliber, a performance comparable to the bigger 120 mm T179. But since the M48 chassis and its armor concept had become outdated by the time, too, the M77A1 fleet was by 1986 fully replaced by the M60A3, the US Army’s new standard MBT.
Crew: 4 (commander, driver, loader, gunner)
Weight: 51 tons
Length: 6.946 m (22 ft 9.5 in) hull only, 10,66 m (34 ft 11 in) overall w. gun forward
Width: 3.63 m (11 ft 11 in)
Height: 3.08 m (10 ft 1 in)
Ground clearance: 1 ft 6.2 in (0.46 m)
Fuel capacity: 385 US gal (1,457 l)
0.5 – 5.3 in (13 – 137 mm)
– Maximum, road: 30 mph (48 km/h)
– Sustained, road: 25 mph (40 km/h)
– Cross country: 9.3 to 15.5 mph (15 to 25 km/h)
– 40% side slope and 60% max grade
– Vertical obstacle of 36 inches (91 cm)
– 102 inches (2.59 m) trench crossing
Fording depth: Unprepared: 4 ft (1.219 m), prepared: 8 ft (2.438 m)
Operational range: 287 ml (463 km) on road
Power/weight: 16.6 hp (12.4 kW)/tonne
1× Continental AVDS-1790-2 V12, air-cooled twin-turbo diesel engine, 750 bhp (560 kW)
General Motors CD-850-3, 2-Fw/1-Rv speed GB
1× 120 mm T179 L/60 rifled anti-tank gun with an autoloader and a total of 29 rounds
1× co-axial 7.62 mm M240C machine gun with 3.000 rounds
1× .50 cal (12.7 mm) M2 Browning (600 rounds) or .30 cal (7.62 mm) M73 machine
anti-aircraft machine gun (1.000 rounds) on the commander’s cupola with 600 rounds
The kit and its assembly:
This is another fictional creation, but, like many of my whif builds, it is rooted in reality and an extrapolation of what could have been. The oscillating tower with the M103’s 120 mm cannon and an autoloader was actually developed, and there were several tank projects that made use of it. The T77 was the final proposal, but, like the T57 on the M103 basis and other designs from the Rheem Company, the T77’s development was arduously slow, so that the project was finally canceled in 1957 by the US Ordnance Department. Two turrets were actually built, though, but they were scrapped in February 1958, and the T77 only existed on paper or in model form.
The impulse for this build actually came from a 1:72 resin turret for the T57 project from ModelTrans/Silesian Models. I found the concept cool and the turret had a very futuristic look, so that I bought a set with the vague intention to use it for a mecha conversion someday. Then it gathered dust in the stash, until I recently stumbled upon the 1:72 M103 kit from Dragon and considered a T57 build. But this kit is very rare and expensive, at least here in Germany, so I shelved this plan again. However, I started to play with the idea of a U.S. Army vehicle with a Rheem Company turret. Then I found a Revell M60 kit in the stash and considered it for a whiffy build, but eventually rejected the idea because a turret concept from the late Fifties would hardly make its way onto a tank from the late Seventies or later. When I did further research concerning the Rheem turret, I came across the real T77 project on the basis of the M48, and dug out an ESCI M48A5 from the pile (realizing that I had already hoarded three of them…!), so the M77 project was finally born.
Otherwise, the build was a straightforward affair. The T57 turret is a massive resin piece with a separate barrel and very fine surface details. Some of them, delicate lugs, were unfortunately broken off, already OOB but also by me while handling the pieces. They could be easily replaced with brass wire, though, which was also used to add small rails to the collar. The very long and thin barrel was replaced with a white metal aftermarket piece. It’s actually a barrel for a Soviet T-10 with a complex muzzle brake (made from brass), but the size was just fine and looks very good on this fictional tank.
Some details were added to the turret or transplanted from the M48 kit, e. g. the prominent IR searchlight or the machine gun on the commander cupola. Furthermore, I added a textile seal to the gap between the turret sections and to the barrel’s root, made from paper tissue drenched in thinned white glue. The same method was used to create the searchlight cover, too.
Since the turret base had a smaller diameter than the M48’s attachment opening, I had to improvise a suitable adapter with styrene strips. The M48A5 hull itself was taken OOB.
Painting and markings:
I was happy that I could place this model into a later time frame, so that the U.S. Army’s uniform Olive Drab times were already over. In the 1970s, the US Mobility Equipment Research & Design Command (MERDC) developed a system of camouflage patterns for US Army vehicles. These consisted of a set of standardized patterns for each vehicle, to be used with a set of twelve colours. The local terrain conditions and colours decided which of the paints were to be used, and on which parts of a vehicle. Then, if conditions altered, for example by a change in the weather, or by the unit moving into a new area of operations, the scheme could be quickly adjusted to suit them by replacing only one or two colours by different ones.
For example, if a vehicle was painted in the US & European winter scheme, which had a dark green and a medium brown as its predominant colours, and it started to snow, by overpainting either the green or the brown with white, one of the two snow schemes could be created. This gave a high degree of flexibility, though in practice it was hardly ever actually made use of—most vehicles were painted in one scheme and kept that.
I gave the M77 the “Winter Verdant” MERDC scheme, which was frequently used in Germany. It consists of Forest Green (FS 34079), Earth Red (FS 30117), Sand (FS 30277) and Black (FS 37038). The pattern itself was adapted from the standardized M60 MERDC scheme. Colors used were ModelMaster 1701 and 1710, plus Humbrol 238 and Revell 06. The seals on the turret and the searchlight cover were painted in a faded olive drab, the track segments with a mix of iron, dark grey and red brown.
After basic painting with brushes, the kit received a washing with thinned black and red brown acrylic paint. Decals (taken from the ESCI kit) came next, then the model received an overall dry brushing treatment with Humbrol 72 (Khaki Drill) and 168 (Hemp). Finally, everything was sealed with matt acrylic varnish from the rattle can and the lower hull areas were dusted with mineral pigments, simulating dust and mud.
Another relatively simple conversion, since only the (oscillating) turret was swapped. However, I was skeptical at first because the turret was originally intended for an M103 hull – but mounting it on a smaller M48 chassis worked well, just like in real life!
Posted by dizzyfugu on 2019-10-04 16:38:39
Tagged: , 1:72 , M77 , M48 , T59 , T77 , T57 , patton , tank , oscillating , turret , 120mm , rheem , company , prototype , fictional , whif , what-if , germany , berlin , merdc , winter , verdant , cold , war , modellbau , dizzyfugu , conversion