These are the classic twin-rotor helicopters made for years by Boeing Vertrol and now Columbia Helicopters is in the process of beginning production of this series of helicopters. These are very large complex helicopters, phenomenally expensive to own and operate and as one unidentified military pilot said about a CH-47, "If it's not leaking gallons of hydraulic fluid in the back, then there's something wrong with it."
In the bush these helicopters are used almost exclusively for commercial logging and heavy construction.
The picture above shows two different models of the Boeing Vertrol helicopters; the civilian equivalent of the Sea Knight in the foreground and the civilian equivalent of the Chinook in the background.
On the military front, the following video clip is a very cool display of a Navy SEAL boat making a quick exit via Chinook. Now it should be pointed out that there has been some "e-bitching" about whether this video features a Chinook or a SeaKnight. Quite frankly, the video is from the inside of the bird so its hard to tell. But, here are some pointers from an Army flight engineer:
How to tell this is in fact a CH-47 is:
The Chinook in the next video does some impressive fancy flyin'.