Blitzo...indeed, howitzers are included, but not to be discounted are the 15 inch naval guns. One needs quite a stable platform to mount those puppies on, however. Additionally, hearing protection is much advised.
In all seriousness, though, this page is an abbreviated version of what C&R's are all about...aka "Cruffling". Depending on your enthusiasm with historical and vintage military arms, and, of course, your local and state laws dictating eligibility, I highly recommend you check it out. Most everyone will warn you, however, that once you begin, your bank account soon will be for naught.
It certainly is entertaining, however, and you can post your newly acquired purchases on this website and get all kinds of excellent information from many knowledgeable collectors.
http://www.cruffler.com/whatis.html
Also...if you want to get involved in collecting, check out this useful page:
http://www.cruffler.com/becomingcruffler.html