The British <a href="https://en.wikipedia.org/wiki/en:PIAT" class="extiw" title="w:en:PIAT">PIAT</a> anti tank weapon.  This particular gun is part of an interactive display at the <a href="https://en.wikipedia.org/wiki/en:Museum_of_Army_Flying" class="extiw" title="w:en:Museum of Army Flying">Museum of Army Flying</a>, Hampshire, UK.
<a href="//commons.wikimedia.org/wiki/User:Ranger_Steve" title="User:Ranger Steve">Ranger Steve</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>