Bouton Paul Mk1 Defiant turret.
RAF
circa 1940 <div style="display: none;">date QS:P,+1940-00-00T00:00:00Z/9,P1480,Q5727902</div>
<a rel="nofollow" class="external text" href="http://www.wwiivehicles.com/unitedkingdom/aircraft/fighter/boulton-paul-defiant.asp">photo</a>