Sea Knight

what is the difference between the army chinock and the marines sea knight ?

The CH-47 (Chinook) is a heavy lift helicopter used in the army. I don't know the exact numbers for the Chinook, but it's max gross weight is somewhere above 50,000 pounds. They can probably carry about 30 troops. At first glance it looks very similiar to it's smaller brother the Sea Knight.

The CH-46 (Sea Knight) is a medium lift helicopter used by the Marines with a max gross weight of 24,300 pounds. It can carry about 3000 pounds of cargo, or roughly 12 combat loaded Marines. The Marine Corps has the CH-53 for heavy lift. So, what good is the smaller CH-46? It is much more reilable than the CH-53 and cheaper to operate. It is used primarily for troop transport and casevac, as it is able to fit into smaller zones than the heavies and can make faster approaches into a zone as it can decelerate quicker. It has a much better defensive suite (infrared-jammer, missile warning system, armor protecting engines and flight controls, etc.), and .50 cal door guns, making it more survivable in a hostile area.

How can you tell the difference between the two?
There are two easy to identify features.
1. The CH-47's engines are mounted externally on pylons on the tail. The engines on the CH-46 are mounted internally with only the exhausts sticking out the sides.
2. The CH-47 has 4 wheels, while the CH-46 is a tricycle set-up.

Rotorfest 2008 - CH-46 Sea Knight Demonstration