Clarification time: the chickens had better not be frozen at the time they're fired from the cannon.
There's a story1 attached to this. Some (but not too many) years ago, British Rail borrowed a chicken cannon from the folks at BAe for the purpose of testing the windshields of the new high-speed trains. They dutifully followed instructions, setting up the cannon and loading it with supermarket chickens.
The first chicken fired completely shattered the windshield and embedded itself in the aft wall of the engineer's compartment.
Seeing this, the train guys called up the aerospace guys who had lent them the cannon and described what had happened. They got the following response:
"Did you thaw the chickens first?"
Incidentally, there are at least two models of chicken cannon in use in the aerospace industry. The first, described in the original writeup, fires single chickens weighing up to 8 pounds, to simulate the impact of one large bird. Another model can only handle birds up to 2 pounds (Cornish game hen time), but it can fire 8 or so of them in the space of 5 seconds, to simulate a flock. Yes, it's a chicken machine gun2, or its nearest equivalent.
In addition to testing windshields and other structural elements, chicken cannons are standard testing gear for turbine engines. A bird (or flock) sucked into a jet engine is a Bad Thing if the first-stage compressor blades aren't designed to withstand the impact.
1Okay, so this has been revealed to be an urban legend.
2In my college days, I often wanted to introduce this into a Paranoia campaign as a weapon, but I couldn't justify the existence of frozen chickens in Alpha Complex.