A clothing history query Index finger gloves

[Moondog55]

Calling them index finger gloves may offend fewer people than calling them trigger finger gloves
When I was in the UK decades ago there were many Airforce "Mountain Rescue overgloves" sold as surplus and that was where I first saw them but I never saw a dedicated trigger finger glove until I became familiar with the American woollen M-65 liners

The collective wisdom of the forum may be able to help me before I head off to Professor Google.
Where and when did the index finger/ trigger finger glove [ or mitten if you prefer] originate?
My quick searching would indicate Labrador but that was a really quick look around the internet.
Were they common before WW1 or even WW2?
I've seen may trigger finger shell mitts from WW2 but the British/Commonwealth ones seem to have been made and used to go with normal type woollen gloves not ones with a separate integrated index finger