Nothing is written in Wikipedia on how the engines of the De Havilland Comet or other similar airliners were started. However, it seems that aircraft of this generation could not start the engines stand-alone without the ground support, and that the Boeing 727 in 1963 was the first jetliner capable of doing this.
In one of the answers Terry describes technicians suffering desperately while attempting to start 747 with the two old ground-based devices. From this it looks like while "theoretically possible", this was a very uncommon and unexpected task for them.
Since when are ground based starting devices no longer in common use? Are there still any jetliners in service that would require them?