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Close up as mounted on a SE5a
http://c7.alamy.com/comp/GHK6K8/se5a-of-the-shuttleworth-collection-at-old-warden-GHK6K8.jpg
Some of the early aircraft mounted the Lewis above the wing, before the Foster mount was thought of.
In those aircraft the pilot had to unstrap, stand up, while holding the stick somehow, and change that drum.
The double drum held over 90 rounds, so you didn't change it often.
I wonder how the pilot managed that rear firing Lewis on the B.E.12 ?
It had to be pretty hard to aim looking over your shoulder .
wow, a four blade prop on the se5a!!!!!!