Fuel

[Panzer]

Well, in a way, each lifeform is a machine, only made of proteins (or whatnot) instead of metal. The nomad battleships required a shipyard to be built (remember that mission in Rheinland, with von Claussen?). This implies, that they're either vesles like the human ones OR as StormHawkesaid, specially bred(dunno if the right word for this) hosts for the nomads (or nomad brains).

Current knowledge in the field is merely based on in-game observations, not detailed data, made by the game's creators (maybe they just needed weird, dangerous, ugly and "killable" aliens as they are, not a whole advanced alien race, with all their details, anathomy, history and species info as they'd be useful now)

---