ROBOTECH Technical Files
by Pieter Thomassen


Sian Dereta class Border Fleet battlefortress

Robotech Masters
Sian Dereta
Naval Separator

Name and disposition:

Ship's complement:


Propulsion systems:

Endurance and mobility limits:

Weapon systems:

Air group and mecha complement (typical for Border Fleet, 1995):

Tirolian forces:
Zentraedi forces:


Design notes:

The Sian Dereta class was designed specifically for the demands of the Border Fleets. As such, the design differed considerably form the Zentraedi refits that had, to that time, made up the bulk of the Border Fleet strength.

A primary difference with ships such as the Queadol-Magdomilla was, for instance, the provision for a mostly Tirolian crew, with the Zentraedi giving troop and heavy labor duties labor only. Of course, due to their bulk, the Tirolian living spaces were still considerably smaller than those for the Zentraedi. This had still considerable effects on the design. Furthermore, the whole emphasis of the vessels was shifted from general duty police and space control to anti-ship and planetary bombardment taskings, in addition to greatly improved sensor performance. Moreover, great attention was given to prolonged deployments without, or with only minimal, support from faraway home bases.

As with all Zentraedi Reflex cannon ships, the front section of the Sian Dereta composed the main armament. The class was unique in carrying a double Reflex cannon, rather than a single. This was not done to improve firepower, as the powerplant could not recharge the two cannons simultaneously, but because these ships were to operate farther away from support forces and structures. The second cannon then was carried to reduce wear and tear and for redundancy. However, the advantages of this 'spare cannon' proved to be so small in relation to material effort of building and operating the weapon that in the successor class, the Sian Macross, the double cannon was deleted and a single cannon carried once again. The lower levels of the cannon booms carried the Zentraedi mecha hangars and some personnel quarters, with launch bays opening on the open bay in the middle of the booms.

The center section of the ship was the main structural member. The dorsal carried the Tirolian command citadel, a cilindrical structure lying on the hull, tipped aft by one of the secondary engines. The upper levels of the main section proper were dedicated to the Tirolian crew quarters and supprt systems, followed by two large and deep decks for part of the Zentraedi complement. On these levels was also the fold system hold. The lower levels were hangar decks for the smaller ships, almost exclusively Tirolian Assault Corvettes, though some Zentraedi shuttles and drone mining craft were also carried. The hangar decks were served by a large closeable ventral hatch in the center of the main section.

Flanking the main section were the two engine sections, which continued with the engines proper aft of the main section. The forward parts of the engine sections housed in their upper levels the various large installations such as the fabrication equipment and fuel purifiers. The center levels housed the Reflex furnaces and heavy engineering equipment, while the forward lower levels housed the Tirolian troops (with launch chutes for the Bioroid mecha). Aft of these primary engineering spaces were the reaction engines proper. Spreadout thoughout the ship were the reaction mass tanks for the ship and attached craft and mecha.

The Sian Dereta's engine sections were typical of older Border Fleet designs, and were flanked by outrider bodies with the more sensitive sensor equipment. Apart from isolating these sensors from the ship proper, these sections also covered the main engineering spaces from flank attacks. The sensors mounted were rudimentary fold sensors and very sensitive EM sensor arrays. These were supported by additional sensor booms at the tip of the cannon booms.

The Sian Dereta carried a heavy armament. Apart from the double Reflex cannons already mentioned, the ships mounted eight heavy particle cannons, more than the larger Queadol Magdomilla assault cruiser. These cannons were located in the tip of the cannon booms (2), in elevating mounts on top of the cannon booms (2), and in blisters above and below the main reaction engines (4). This meant that usually five or six heavy cannons could be brought to bear on an enemy ship, given the customary Tirolian tactic of pointing the ship at the enemy to deny him a large target area. Consequently, the ventral engine cannons were relatively useless, and in the succesor design, the Sian Macross, these cannons were moved to the upper forward deck (Terran derivatives of the Sian Macross such as the Valiant class have this reversed, as those ships serve as the main capital ships and not as a design for use with numerical and technological superiority). The medium and missile defense batteries were as heavy as those on Zentraedi ships half again the Sian Dereta's size. All this weaponry had its price, of course. The torpedo armament was minimal, certainly compared to what Zentraedi ships carried, but the heavy cannon armament compensated for this. The troop capability was reduced even more, but this too was acceptable as the Border Fleet was not intended to assault or police planets.


In 1653, the Robotech Mercantile Empire had expanded to such a size that supply lines to the outlying territories, thinly populated with troops but always under a greater threat than the inner regions, had become cumbersome to maintain. In addition, although the communication equipment allowed real-time contact with Tirol, the Zentraedi and Triumviroid headquarters there lacked in 'on site' awareness. What was needed was a flexible, semi-autonomous combat force capable of dealing with threats on the Empire's rim on its own or, at least, of sending a warning and holding the line until reinforcements arrived.

Built to fulfill this need were Border Fleets. Unlike the regular Tirolian and Zentraedi fleets, these fleets were made up of mixed Tirolian/Zentraedi crews, operating custom-designed ships with a large amount of autonomy. The Triumviroids commanded the ships and Task Forces, clone forces provided a fast reaction force and Zentraedi troops provided the heavy troop component. Because these forces had to operate in distant areas without the certainty of fast reinforcements the troops were equipped with a qualitatively superior weapons mix compared to the core imperial forces. For instance, the Zentraedi Borderers, as they were often called, were equipped with 7 times the normal allotment of Glaug pods, and were also among the first units to receive Quaedluun-Rau power suits.

This qualitative edge also extended to the Border Fleet ship designs. The Border Fleet's largest ship was designed as the Sian Dereta class battleship, but after the designers recognised that its mission profile and outfit were different from all ship classes that had gone before the designation was changed to the new 'battlefortress' category, incidentally effectively deleting the battleship designation. As the first class to be so named, the Sian Dereta set the standard for these ships, a standard which these days becomes more and more the standard for all capital ships. This includes Reflex cannons as the main weapons, supported by an anti-ship cannon armament heavier than a Queadol Magdomilla assault cruiser. The medium cannon and missile batteries were as strong as the Thuverl Salan's, a ship almost half again as long as the Sian Dereta.

The first Border Fleet ships were converted Zentraedi vessels, and the first Sian Dereta prototype entered service around 1680. The Sian Dereta served with the Border Fleet as the local flagship, usually leading a task force of Seron Thoun battlecruisers and a number of Tou Redir scout vessels (and later, Tou Salaam class Exploration cruisers), all accompanied by one or two Quiltra Queleual vessels in the supply configuration. These task forces each patrolled their area of the Empire's border sectors, scouting for threats and generally giving acte the presence for the Tirolian Empire. With an average of one Sian Dereta and five Seron Thoun ships in each task force, the battlegroups were highly potent, numbering an average of seven Reflex cannons between them. In addition to the larger than usual amount of anti-ship weapons this gave the task forces the firepower equivalent of several Zentraedi battlegroups of equal size. However, while the troops stationed on the ships were fast and hard-hitting, they were not as numerous as those on regular Zentraedi ships, and thus the Border Fleets were limited frontier patrol duties and fast strike missions only. Conquest and large scale policing were not part of the Border Fleet tasks and were relegated to the main Zentraedi forces. This ship and troop make up of the Border Fleets, combined with the close Tirolian supervision through the Triumviroid commanders, made such a task force ideal for special forces duties, and the Tirolian fleet command appropriated several Sian Dereta and Seron Thoun groups after construction and employed them as such, though never in numbers exceeding 97 such task forces.

The Sian Dereta continued in series production for near two centuries, with an estimated 80,000 vessels of the class built. In the final years of the 19th century, the Border Fleets were at strength, and attrition could be met for the foreseeable future by ships then under refit and repair, and by replacing losses with Seron Thoun craft on a temporary basis. Due to the independent nature of the Sian Dereta, it was not until about a century later that the class was becoming a thinly spread design whose replacement parts were no longer in production and whose stocks were dwindling. Rather than rebuilding the production lines, a new and updated design, the Sian Macross, was prepared and construction begun on prototypes, with the goal of replacing the Sian Dereta on a one-to-one basis over the next five to seven decades. However, protoculture depletion and the disaster regarding Zor made this plan impossible. The Sian Deretas, like all Tirolian ships, gradually lost power in the first two decades of the 21th century, and were destroyed outright or stranded in place at their farflung postings.

As an historical note it should be mentioned that the RDF used the outer hull of one such ship, captured (as a total loss) in 2015, as the outer hull of the SDF-3 Pioneer, which was built to the exterior dimensions of the Sian Dereta class. The Pioneer thus almost perfectly mimicked a Sian Dereta, as part of a ploy to close with Tirol before being fired upon. As another point of interest it must be stated that the Border Fleet designs lend themselves admirably to adaptation as capital ships for Terra and her allies. This was due to the heavy armament on a relatively small hull, coupled with the large troop capability created by replacing full size Zentraedi with micronian sized troops.

See additional design notes.

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Robotech (R) is the property of Harmony Gold. This document is in no way intended to infringe upon their rights.

Content by Pieter Thomassen
HTML by Robert Morgenstern (
Copyright © 1999 Robert Morgenstern, Pieter Thomassen, Peter Walker

Robotech (R) is the property of Harmony Gold. This document is in no way intended to infringe upon their rights.

Content by Pieter Thomassen
HTML by Robert Morgenstern (
Copyright © 1999 Robert Morgenstern, Pieter Thomassen, Peter Walker