Well guys, I took the risk with the air technique, but also bore in mind Marc's guidance, so made sure I was as delicate as possible...
Crystal came out with no damage and I was able to fully reassemble the watch.
Thank you to everyone that took the time to give advice, very much appreciated.
One last thing, on the watch the second hand is the lower sub-dial, the large second hand is a chronograph.
This watch was repaired a number of years ago and when it was returned the chronograph hand was at the 3rd increment, instead of at 12.
When I reassembled the watch today I took care to place all hands pointing towards 12. I started the chronograph and it jumped back to the 3rd increment and stopped moving. Starting it again it works as normal, but again from the 3rd increment. Reseting the chronograph the hand returns back to the third increment, like in the attached photo.
Any idea what may be causing this?
The crystal is domed glass, apparently sapphire.
There also seems to be no bezel on the watch, the case is one piece with no distinguishable seem where a bezel will attach.
I suspect that the crystal is press fit into the case.