Chula

The Chula were a race of aliens encountered by Jack Harkness and known to the Ninth Doctor.

Culture
In common with many other species, the Chula spacecraft used mauve alert to indicate the highest level of emergency. (TV: The Empty Child)

Technology
The Chula used spaceships for both warships and ambulances. They also had nanogenes, which they used in wars to heal and reconfigure their soldiers. These nanogenes were mainly for use on Chula soldiers, which meant they had trouble healing newly encountered species. Chula ships also used a device capable of producing a tractor beam, the visual effect of which was a long blue energy tube with pulsing rings of lighter blue energy moving along it. (TV: The Empty Child/The Doctor Dances)

History
Jack Harkness stole an ambulance and a Chula warship. He used the ambulance to lure the TARDIS (which he thought contained Time Agents) and landed it in 1941 London. He wanted to con the "time agents" into thinking it was a Chula warship, and made sure a German bomb was to land on it, obliterating it. (TV: The Empty Child) Little did he realise the nanogenes would escape and cause the Empty Child plague.

The Ninth Doctor destroyed the ambulance so it couldn't cause any more trouble. Jack Harkness disposed of the bomb by pulling it into his warship and escaping. The warship was later destroyed by the bomb. (TV: The Doctor Dances)

Behind the scenes

 * Writer Steven Moffat got the word Chula from a restaurant in London. (DWDVDF 5)