When the DDS fleet was expanding in the early 2100s it was clear that a fleet of replenishment ships would be required. Naturally the then in development SUP (Standard Utility Platform) was used as the basis for this new ship and in 2105 the first Extender entered service. Since then the Extender fleet has put in the hard light years, supporting DDS ships away from base no matter where they may be. An Extender always accompanies a DDS deployment. Extenders, which are of course huge ships, also include extended leisure facilities to "refuel" ship crews also.
At the time of writing there are 17 Extenders in service with 4 more on order. The expanding DDS fleet and increased frequency of deployment means that the Extender fleet may have to keep growing even beyond that. Such is the intensity of their workload that an update of the earliest few ships had been postponed for a year as the fleet simply could not operate if it had to lose a few Extenders for a month each! It is hoped by this time next year the fleet will be large enough to finally release the pressure.