WTF???

[HoosierAnnie]

Is this some sort of artillery chronometer??

 

[policemedic]

I don't know, but I want one.

 

[SpitfireV]

I don't know, but I want one.

You'd barely touch the sides

 

[AWP]

My guess (too lazy to Google) is a "suppressor" for testing/ training, a method of reducing the audio output of the howitzer.

 

[TheSiatonist]

^^Right on the money, Free.

http://www.thefirearmblog.com/blog/2009/10/16/worlds-largest-gun-suppressor/