O17

O17
O17 parade through Yaoyotepec outer ring.
Type	Main battle tank
Place of origin	Zacapican
Production history
Designer	NTT 114
Manufacturer	ACQZ Armor Works
Produced	2017–present
No. built	81 units 120 total by 2025 (planned)
Specifications
Weight	55 tonnes
Width	3.5 m (11 ft)
Height	3.3 m (11 ft)
Crew	3
Armor	13-44-AB Composite
Main armament	610-ZZZT 125 mm (4.92 in) smoothbore cannon with 45 rounds (32 of them in the autoloader).
Secondary armament	12.7 mm (0.50 in) Quetzal (6P49), 7.62 mm (0.30 in) Xiuhcoatl
Engine	Diesel 1,200/1,350/1,500 hp
Power/weight	31hp/t
Transmission	12-speed automatic gearbox
Operational range	min 500 kilometres (310 mi)
Speed	80 km/h (50 mph)–90 km/h (56 mph)

The O17 is a Zacapine main battle tank based on the experimental platform Tepoztetl-100 designed in the 1980s, and the Tepoztetl-41 from the 1950s. It was formally adopted by the Zacapine military in 2017, with a test batch of 15 units already in service while delivery for the main production run of 65 O17s is expected to begin in 2025. The O17 is considered to be a next generation armored vehicle and represents the most sophisticated piece of equipment in service with the Zacapine ground forces, rivalling many naval and aerial projects in other branches of service. As a result of the extensive technical and financial requirements of the project, the development of "Tepoztetl-121" has been ongoing for 25 years and has become the central project of the Zacapine army's development wing under the NTT program for the better part of a decade.

Development History

Development of what is now the O17 began in 1997 under the designation Tepoztetl-121 at the NTT 114 design unit located in Amegatlan. The orders to come up with an entirely new tank project followed on the heels of four years of debate following a 1993 report showing that the turret was the most often targeted and hit part of any tank, as it would often be the first part of the tank to become visible to an enemy as it navigates terrain. The same study found that the O74Y tanks in service, despite being upgraded with improved explosive reactive armor protection, were critically flawed due to the increasingly inadequate quartz filled cavity composite armor design of the underlying turret which was the standard for the O74, the basis for the O74Y modernization. This report convinced the designers and military officials in control of the Zacapine armored forces that it was necessary to develop an entirely new design rather than another O74 modernization, one that would prioritize a smaller, better protected turret. Initial proposals revolved around a one man turret which would hold only the commander, while the gunner would operate the tank's main weapon from below in the hull. However, this quickly evolved into a concept with an entirely unmanned turret with all crew housed safely in the hull. Designers promised that this would not only improve crew protection, but would allow for a turret with better protection and a much smaller target profile.

Preceding Designs

Armored vehicle concepts with unmanned turrets had been proposed twice before, both times by the NTT 114 design team. The first was a concept for a self propelled gun proposed in 1955, designated Tepoztetl-41, with a completely unmanned turret armed with a 105mm howitzer and a crew of four enclosed in the hull. A mockup of the Tepoztetl-41 was built for demonstration purposes but no fully functioning prototype was ever built. The concept would be revived three decades later with the Tepoztetl-100, this time in the form of a main battle tank design armed with a 125mm smoothbore canon. In order for the design to function, the crew had to be positioned directly below the turret, which required the carousel of the autoloader to be removed and a complex mechanism for manual loading of the gun to be implimented. Two examples of the Tepoztetl-100 were built and were functional enough to enter practical testing. However, the Tepoztetl-100 suffered from many serious issues, namely problems with the weak engine, and many complications with the turret control and unusual manual loading system for operating the gun from below. The prototypes were considered unsatisfactory and could not compete with baseline O74 tanks already in service at the time, let alone the O74Y modernization that had just been approved in 1986.

Prototyping Process

Following the release of the 1993 report, the Tepoztetl-100 design was brought back to the drawing board as the Tepoztetl-121 with the expectation that implementing new technology and electronics would overcome the shortcomings of the original Tepoztetl-100 design. What followed was three rounds of redesigns, which produced prototypes designated by their completion date. The Tepoztetl-121-2004 was the first to release and the most flawed of the prototypes, having many of the same problems with turret control and gun operation as it had retained the ancestral layout of the Tepoztetl-100 with the crew underneath the turret. Such a layout was deemed flawed and the 2004 prototype was scrapped and the project again returned to the drawing board. This time, a carousel autoloader system lifted directly from the O74 would be implimented, with the crew moved out from under the turret into the front of the hull with the Tepoztetl-121-2009. The 2009 prototype was much improved with regards to control of the turret, but was deemed in need of modernizations and improvements. This time, the same 2009 prototype vehicle would be directly modified to produce the finished prototype.

The carousel and autoloader were redesigned to house more modern APFSDS ammunition with longer penetrators required to defeat modern composite and explosive reactive armor. Machineguns, which were initially left off the design as they could not be operated by the crew when mounted on the turret, were added using the same remote control technology also implemented with the main gun. Modernized thermals and night vision as well as an improved commander sight and battle management system were among the technological improvements installed in the prototype, which were added on the basis of frequent complaints by Zacapine tank crews with regards to the by then increasingly obsolete and limited O74Y tanks. Many of the systems installed in the final prototype were directly lifted from the O74YZA modernization project running concurrent with the Tepoztetl-121 program. The final improvement added to the design was an hard kill APS, which was chosen in favor of the existing soft kill system used on O74Y and O74YZ. This final prototype, Tepoztetl-121-2015, was subjected to rigorous testing and was eventually approved in late 2015 with a test batch of 15 of the finished Tepoztetl-121 tanks ordered. They entered service in 2017, at which point Tepoztetl-121 was redesignated Octacatl 2017 or "O17"

Design

Armament

The main gun of the O17 is the 610-ZZZT 125mm smoothbore gun, an iterative upgrade to the 600-ZZZT gun used in O74YZ tanks in Zacapine service. One of the hallmarks of the 610-ZZZT mounted in the O17 is the lack of any bore evacuator on the gun, as the unmanned turret of the O17 removes the need to evacuate the potentially hazardous fumes and residue from the gun before the breech opens. The canon is capable of firing the most modern TT-20 APFSDS projectiles with depleted uranium penetrators, as well as air burst high explosive, HEAT projectiles, and a gun-launched ATGM munition. These latter guided missiles are reported to also be effective against low flying aircraft and helicopters and give the O17 some anti-air effectiveness. The secondary weapons of the O17 are a 7.62mm coaxial Xiuhcoatl machinegun mounted in the turret and operated by the gunner remotely, as well as a 12.7mm Queztal machunegin which is mounted above the turret on top of the commander's sight to avoid obstructing the latter's field of view which may be controlled by either gunner or commander. The 7.62mm gun is by standard loaded with 1000 rounds of ammuntition in two 500 round canisters fitted to it within the unmanned turret, while the independently moving 12.7mm gun is fitted with a 400 round canister. The tank crew must exit the vehicle in order to replace these canisters once their ammunition is expended, as the armored capsule the crew is seated in doesn't permit internal access to the inside of the turret or the rest of the vehicle. Anti-aircraft missiles and a 30mm anti-aircraft cannon are proposed to be added as future upgrades for the O17, as they were both features stripped from the 2015 prototype as the design was streamlined.

Protection

The first layer of protection for the O17 consists of its Ehecachimali APS, a Zacapine developed hard-kill active protection system which tracks incoming threats using precise radar and fires countermeasures to destroy them before they strike the tank. This has been proven particularly effective in testing against ATGMs, the most common threat faced by tanks on the modern battefield. As a result, the Ehecachimali protection system is the most sophisticated and the most crucial mounted on the O17, as it is capable of neutralizing most common threats to the tank before they strike the hull. The tank itself is equipped with dual explosive reactive armor on the front, sides and top of the hull and turret to protect from incoming shells or missiles from all frontal angles of attack. The rear quarter of the hull's sides are protected by slat armor added onto the sides compensate for a lack of ERA protection on the rear third of the tank's sides. The rear of the hull has neither ERA nor added slat armor for additional protection. The ERA used the O17 is the new Chalchiuh II ERA which provides an unknown degree of protection against ATGM, HEAT and APFSDS projectiles. It is known to be an imporved system to the Chalchiuh I ERA used on O74YZ tanks, which reduces HEAT and ATGM penetration by roughly half and APFSDS penetration by over 50%, with estimates varying from 55-65%. The underlying composite armor is made of aluminum and plastic composite layers inside an armored shell with a system for controlled deformation. Additional protcection panels with fire retardant properties are mounted around the crew capsule in the hull and surrounding the carousel where the ammunition is stored to improve survivabiluty of the tank in case of penetration.