The system is almost completely internal with the exception of a single tractor beam emitter which protrudes from the spine of the vessel , usually from the aft section of Decks 2 and 3 of the primary hull, an astrometrics lab on the Constitution-class starships. Internally, it is no more than a second tractor beam unit placed just forward of the primary engine room. In older vessels, it is the primary tractor beam unit. Most vessels were upgraded with a forward tractor unit as well in 2255 due to inability to use the tractor beam during warp travel. This tractor beam unit was a duplicate of that found on Constitution-class vessels, except that it was placed on the fore-section of the primary hull.
In the late 2220s, Federation research and development began work on a new series of starships to replace aging and outdated NX-class vessels. R&D began working on a series of vessels, the Constitution class, to be the centerpiece of their design. The design was led by the new Leeding FWG-01 warp nacelle which was expensive, but much more efficient than the earlier type II nacelle.
Because of the expense of these newer nacelles, R&D began looking into utilizing a single warp nacelle variant for lighter service. Trying to find a way to allow balanced warp fields without tandem warp nacelles, the teams looked into using a variety of field generators to push or pull the warp envelope around the ship. The result was the creation of the Doppelganger warp system in 2235.
Early Hermes-class scouts and their counterparts, the Saladin-class destroyers, fitted with the new system, found that the force field generators tended to be faulty and often shorted out, leaving them stranded and in need of rescued. They were also very power-consuming, leaving the destroyers needing more power.
In 2243 the type II Doppelganger warp system began production. Addressing the problems of the earlier type I drive, the type II utilized a much more efficient tractor beam and featured a built-in power doubler, called the "military power overdrive system", which doubled the system's power output at the expense of overall lifetime of the warp engine. Because of the shorter lifetime of the warp engine, the ship usually ran at half power, only calling upon "military power" when full power was called for. This was installed on all new destroyers starting with the USS Tamerlane in 2244.
By 2270 the Doppelganger drive was integrated into the primary systems of all single-nacelled vessels and "military power" was tied to the function of calling a ship to red alert, becoming effectively transparent to day-to-day operation.
The system uses a dedicated tractor beam located on the opposite side of the spacecraft from the unbalanced warp nacelle to in essence pull the warp envelope fully around the vessel, essentially "cloning" the warp field and mimicking a second nacelle, thus enabling a single-nacelle starship to maintain a stable warp field as if it were a dual-nacelled vessel.
Unfortunately, this function tends to drain the engines at slightly less than twice the rate of a standard dual-nacelled vessel. The destroyers and scouts using the Doppelganger warp system were relegated to half-power usage during normal day-to-day operation, with destroyers only being able to bring the ship to full power during combat or while at high warp by using the military power overdrive system. This process was typically called "ordering a ship to military power".
Part of the experiment of the comic Tamerlane was to keep true to canon as much as possible--canon being loosely defined by the author as all things canon and expanded canon, such as technical manuals and novels, though this later included fan films and much of the fan community. The problem is that many times Star Trek canon conflicted with itself. Wanting to hold true to Gene Roddenberry's comment that "All ships must have nacelles in pairs" but also wanting to base the comic on the Saladin-class destroyer designed by Franz Joseph with its single warp nacelle, it became clear that there would be an interesting problem in canon logistics, especially since the ship was canonized in Star Trek II: The Wrath of Khan and Star Trek III: The Search for Spock by appearing on screens in the background. The author needed a compromise between these two seemingly conflicting items. The Doppelganger warp system was devised to explain the discrepancy.