Basically because “Rules of Engagement” is a phrase that has at least two meanings, I decided we needed a story that did touch on the military version of it. Since Jack and Hellina were already on the scene it made sense to place the story on board their ship, the Scorpius. This is the first time I had mentioned the name of the ship that first featured in the Arachnoids story, having been taken over by the Arachnoids. It was not, at that time, named. Nor in any of the other stories in which the 22nd Space Corps helped to save the day. Choosing a name for it was problematic. Most of the good ones seem to be gone already. Stargate SG1 cornered the market with ships like the Dedalus and Prometheus and the various incarnations of Star Trek have well thought out names for their ships. And then there is the Millennium Falcon, and even the Righteous Indignation, the wonderfully named ship of Bucky O'Hare the space bunny of kids cartoon hour. I have had my own share of themes, with passenger ships in my stories being named after science fiction writers – The Aldous Huxley, for example, while hospital ships were named after lady doctors – The Grace Holloway, the Florence nightingale and the Marie Curie. But thinking up a name for a military ship that could measure up to the likes of the Prometheus was hard work. I eventually decided to look at the Zodiac and settled on Scorpius. At the least, it allowed for the throwaway line ‘a sting in its tail’ to describe the thermic torpedoes that settle the battle.
Ambassador Fitzgerald, is a link back to one of my Theta Sigma stories, in which the Fitzegerald clan of 12th century Ireland have to be saved from extinction because their descendents would be important people not only on Earth, (JFK etc.) but in Human colonisation of the galaxies. The enemy, the Sontarans and Rutans, are a traditional pair of foes. They have popped up from time to time in The Doctor’s history, never quite going away. I don’t tend to use existing enemies often. I prefer to make up my own. Hence there have not been any Daleks or Cybermen stories so far in this series. Though watch this space. Both will turn up eventually. Sontarans and Rutans are militants who have read the ‘rules of engagement’ and then used them for target practice. And The Doctor knows that from the start. He expects trouble and is distressed when the Ambassador is the innocent victim of it.
The scene with Rose and Jack rescuing The Doctor from the Sontarans is, of course, a deliberate reversal of the scene at the start of Parting of The Ways in which Jack and The Doctor rescue Rose. That was such a brilliant scene it DESERVED to be reworked.